Transcript Document

Course 6
RAINWATER HARVESTING
Teacher
Saroj Sharma
1
[email protected]
About Saroj Sharma
Saroj Kumar Sharma graduated in Civil Engineering with distinction in
1988 (M.R.Engineering College, University of Rajasthan, India),
completed his MSc in Sanitary Engineering with distinction in 1997
(IHE Delft, The Netherlands) and PhD in Groundwater Treatment in
2001 (Wageningen University and IHE Delft, The Netherlands). He is
specialized in water supply engineering - water quality, treatment and
distribution.
He has 22 years of professional and academic experience in planning,
design, implementation, and operation and maintenance of urban,
semi-urban and community-based rural water supply projects. He has
worked with several government agencies, international consultants
and donors (UNICEF, WHO, ADB, WB) in various water supply
projects in different parts of the world.
His teaching and research interests are in the field of physicochemical
treatment processes (filtration and adsorption based processes),
natural treatment systems (bank filtration and soil aquifer treatment),
water transport and distribution (water loss management, urban water
demand management, corrosion of water pipes) and decentralized
water supply systems for small towns and urban poor areas.
http://www.unesco-ihe.org/iu/staffmember/roj
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Contents
This Course is built up from 5 parts:
1. Introduction
2. Uses, advantages and limitations of RWH system
3. System components and design considerations for roof RWH
system
4. Quality aspects of RWH system
5. Examples of RWH systems
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Part 1
INTRODUCTION INTO
RAINWATER HARVESTING
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Introduction (1)
Rainwater harvesting (RWH): technology used for collecting
and storing rainwater for human use from rooftops, land
surfaces or rock catchments.
One of the world’s most important ancient water supply
techniques (practiced for more than 4,000 years), is beginning
to enjoy a resurgence in popularity.
Rainwater is an important water source in many areas with
significant rainfall but lacking any kind of conventional,
centralised supply system.
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Sigiriya, Sri Lanka.
6
Sigiriya, Sri Lanka. This reservoir cut into the rock was used
centuries ago to hold harvested rainwater.
http://www.itdg.org/html/technical_enquiries/docs/rainwater_harvesting.pdf
7
Cistern of the Maya people,
called Chultun
Capacity: 45 000 Litres
Diameter: 5 m,
Catchment area: 150 m²
Source: http://www.irpaa.org.br
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Introduction (2)
Rainwater is also a good option in areas where good quality
fresh surface water or groundwater is lacking.
It could be used as a supplement to piped water supply e.g.
for toilet flushing, washing and garden spraying
RWH is a decentralised, environmentally sound solution, which
can avoid many environmental problems often caused in
centralised conventional large-scale water supply projects.
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Types of Rainwater Harvesting Systems
1. Roof catchments
•
•
•
Simple roofwater collection system for households
Larger systems for educational institutions, stadiums, airports, and
other facilities
Roofwater collection systems for high-rise buildings in urbanised
areas
2. Ground catchments (man-made)
3. Rock catchments (natural, impervious outcrops)
4. Collection of storm water in urbanized catchments for
recharge
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Typical Domestic Rainwater Harvesting
System
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Source: http://www.eng.warwick.ac.uk/DTU/rainwaterharvesting/index.html
Ground Catchment System
Source: ENSIC (1991)
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Ground
Catchment
System
13
Rock Catchment System
Source: ENSIC (1991)
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Part 2
USES, ADVANTAGES &
LIMITATIONS
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Use of Harvested Rainwater
 Non-potable purposes (mainly in urban areas)
- Gardening
- Flushing
- Washing clothes/cars
 Potable purpose after ensuring quality
(mainly in rural and peri-urban areas)
16
Small-scale rainwater harvesting systems and
uses
17
RWH in Urban Areas
In view of increasing migration to urban area and the emergence of
mega-cities in the next millennium, it is imperative that water supply
systems should be evolved to cater for such a development.
In areas with relatively high rainfall spread throughout the year, where
other water resources are scarce, RWH is an important option, for
example parts of Sri Lanka, Philippines, Indonesia, Nepal and Uganda.
Installation RWH system is mandatory for the construction of buildings
in some towns in India and on the Virgin Islands, USA.
Many government agencies and municipalities worldwide provide
grants/subsidies and technical know-how to promote RWH system.
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RWH in Urban Areas (2)
 In case of roof catchment systems, there is sufficient
flexibility to utilize systems that will be adaptable to suit all
socio-economic levels of population including the urban poor.
 Examples of typical options in urban area
- Rainwater use in households as a supplement
- Public institutions
- High rise building in high density urban areas
- Collection of rainwater in industrial areas
- Use of runoff in airports
- Collection of rainfall from public open spaces for
recharging
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Advantages of RWH
 RWH systems provide water at or near the point where water is
needed or used.
 Rainwater is relatively clean and the quality is usually
acceptable for many purposes with little or even no
treatment.
 System is independent and therefore suitable for scattered
settlements.
 Local materials and craftsmanship can be used in construction
of rainwater system.
 Ease in maintenance by the owner/user
 Provides a water supply buffer for use in times of emergency or
breakdown of the public water supply systems
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Advantages of RWH in Urban Areas
 Flood control - by greatly reducing urban runoff;
 Stormwater drainage - by reducing the size and scale of
infrastructure requirements;
 Firefighting and disaster relief - by providing independent
household reservoirs;
 Water conservation - as less water is required from other
sources;
 Reduced groundwater exploitation and subsidence - as less
groundwater is required;
 Financial savings – where rainwater can be used in place of
water purchased from water vendors.
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Limitations of RWH
 The initial cost (mainly of storage tank) may prevent a
family from installing a RWH system.
 The water availability is limited by the rainfall intensity
and available roof area.
 Mineral-free rainwater has a flat taste, which may not be
liked by many.
 The poorer segment of the population may not have a
roof suitable for rainwater harvesting.
 Domestic RWH will always remain a supplement and not a
complete replacement for city-level piped supply or supply
from more ‘reliable’ sources.
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Part 3
USES, ADVANTAGES &
LIMITATIONS
23
Part 3
SYSTEM COMPONENTS AND
DESIGN CONSIDERATIONS
24
RWH System Components
 Catchment Area/Roof





- the surface upon which the rain falls
Gutters and Downpipes
- the transport channels from catchment surface to storage
Leaf Screens and Roofwashers
- the systems that remove contaminants and debris
Cisterns or Storage Tanks
- where collected rainwater is stored
Conveying
- the delivery system for the treated rainwater, either by
gravity or pump
Water Treatment
- filters and equipment, and additives to settle, filter, and
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disinfect
Design considerations for rooftop catchment
systems (1)
 The material of the catchment surfaces must be non-toxic and
not contain substances which impair water quality.
 Roof surfaces should be smooth, hard and dense since they
are easy to clean and are less likely to be
damaged and shed
materials into water
 Precautions are required to prevent the entry of
contaminants into the storage tanks.
No overhanging tree should be left near the roof
The nesting of the birds on the roof should be
prevented
A first flush bypass such as detachable downpipe
should be installed
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Design considerations for rooftop catchment
systems (2)
 All gutter ends should be fitted with a wire mesh
keep out leaves, etc.
screen to
 The storage tank should have a tight-fitting roof
excludes light, a manhole cover and a flushing pipe
of the tank.
that
at the base
 The design of the tank should allow for thorough scrubbing
of the inner walls and floor or tank bottom. A sloped bottom and
a provision of a sump and a drain are useful for collection and
discharge of settled grit and sediment.
 Taps/faucets should be installed at 10 cm above the base of
the tank as this allows any derbis entering the tank to settle on
the bottom where it remains undisturbed, will not affect the
quality of water.
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Factors affecting RWH system design
 Rainfall quantity (mm/year)
 Rainfall pattern
 Collection surface area (m2)
 Runoff coefficient of collection (-)
 Storage capacity (m3)
 Daily consumption rate (litres/capita /day)
 Number of users
 Cost
 Alternative water sources
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Feasibility of Rainwater Harvesting

The technical feasibility of roof RWH as a primary
source of water is determined by the potential of a
rainwater to meet the demand more effectively than
other alternatives.

Often the attraction of RWH may be as a
supplementary water source to reduce the pressure
on a finite primary source or as a backup during the
time of drought or breakdown.

The total amount of water that is received in the
form of rainfall over an area is called the rainwater
endowment of that area.

The collection efficiency accounts for the fact that
all the rainwater falling over an area cannot be
29
effectively harvested.
Feasibility of Rainwater Harvesting

The size of supply of rainwater depends on the
amount of rainfall (R), the area of the catchment (A)
and its runoff coefficient (C).

An estimate of mean annual runoff from a given
catchment can be obtained using the equation:
S =R *A*C
Where
S = Rainwater supply per annum
R = mean annual rainfall
A = Area of the catchment
C = Runoff coefficient

The actual amount of rainwater supplied will ultimately
depend on the volume of the storage tank or reservoir.
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Catchment Area Size

The size of roof catchment is the
projected area of the roof or the
building’s footprint under the
roof.

To calculate the catchment area
(A), multiply the length (L) and
width (B) of the guttered area. It
is not necessary to measure the
sloping edge of the roof.

Note that it does not matter
whether the roof is flat or
peaked. It is the “footprint” of the
roof drip line that matters.
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32
Characteristics of Roof Types
Type
Runoff
coefficient
Notes
GI sheets
> 0.9
Excellent quality water. Surface is smooth and
high temperatures help to sterilise bacteria
Tile
(glazed)
0.6 – 0.9
Good quality water from glazed tiles.
Unglazed can harbour mould
Contamination can exist in tile joins
Asbestos
Sheets
0.8 – 0.9
New sheets give good quality water
Slightly porous so reduced runoff coefficient and
older roofs harbour moulds and even moss
Organic
(Thatch)
0.2
Poor quality water (>200 FC/100ml)
Little first flush effect; High turbidity due to
dissolved organic material which does not settle
Source: http://www.eng.warwick.ac.uk/dtu/rwh/components2.html
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Example 1:
For a building with a flat roof of size 10 m x 12 m in a city with the
average annual rainfall of 800 mm
Roof Area (A) = 10 x 12 = 120 m2
Average annual rainfall (R) = 800 mm = 0.80 m
Total annual volume of rainfall over the roof
= A * R = 120 m2 x 0.80 m = 96 m3 = 96,000 litres
If 70% of the total rainfall is effectively harvested,
Volume of water harvested = 96,000 x 0.7 = 67,200 litres
Average water availability = 67,200 / 365 ~ 184 litres/ day
34
Storage System

There are several options available for the storage
of
rainwater. A variety of materials and different
shapes of
the vessels have been used.

In general, there can be two basic types of storage
system:
- Underground tank or storage vessel
- Ground tank or storage vessel

The choice of the system will depend on several
technical and economic considerations like, space
availability, materials and skill available, costs of
buying a new tank or construction on site, ground
conditions, local traditions for water storage etc.
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Storage System

The storage tank is the most expensive part of any
RWH system and the most appropriate capacity for
any given locality is affected by its cost and amount
water it is able to supply.

In general, larger tanks are required in area with
marked wet and dry seasons, while relatively small
tanks may suffice in areas where rainfall is relatively
evenly spread throughout the year.

Field experiences show that a universal ideal tank
design does not exist. Local materials, skills and
costs, personal preference and other external factors
may favour one design over another.
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of
Requirements for Storage System

A solid secure cover to keep out insects, dirt and
sunshine

A coarse inlet filter to catch leaves etc.

A overflow pipe

A manhole, sump and drain for cleaning

An extraction system that does not contaminate the
water e.g. tap/pump

A soakaway to prevent split water forming puddles
near the tank.

Additionally features
- sediment trap or other foul flush mechanism
- device to inside water level
in the tank
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38
39
40
RWH Brick Jars - Uganda
Source: Rees and Whitehead (2000), DTU, University of Warwick, UK
41
Rainwater Harvesting - Kenya
Source: John
42 Gould (Waterlines, January 2000)
Ferro-cement jar
for rainwater
collection Uganda
Source: DTU, University of
Warwick (September 2000)
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Underground lime and bricks cistern
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Rainwater Harvesting – Sri Lanka
45
46
47
http://www.greenhouse.gov.au/yourhome/technical/pdf/fs22.pdf
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A wooden water tank in Hawaii, USA
Source: Rainwater Harvesting And Utilisation. An Environmentally Sound Approach for
Sustainable Urban Water Management: An Introductory Guide for Decision-Makers. ITEC,
UNEP, Japan
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50
http://www.arcsa-usa.org/
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Rainwater Tanks
Source: http://www.greenhouse.gov.au
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Storage capacity

When using rainwater, it is important to recognize
that the rainfall is not constant through out the
year; therefore, planning the storage system with
adequate capacity is required for constant use
of
rainwater, even during the dry period.

Knowledge of the rainfall quantity and seasonality,
the area of the catchment surface and volume of
the storage tank, and quantity and period of use
required for water supply purposes is critical.

There are two commonly used method to
storage requirements.
53
an
estimate
Storage capacity
Method 1 – Storage required for dry period

A rough estimate of the maximum storage
requirement can be made based on the (i) per
capita consumption (ii) no of users and (iii) length of
the longest dry period
 For a household with a 5 people, assuming water use
of 20 lpcd and if longest dry period is 30 days and
rainwater is the only water source,
storage required
= 5 x 20 x 30 = 3000 litres
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Storage capacity
Method 1 – Storage required for dry period

This simple method assumes sufficient rainfall
and catchment area which is adequate, and is
therefore only applicable in areas where this is
situation.

It is a method for acquiring rough estimates of
tank size.
55
the
Storage capacity
Method 2 – Based on rainfall and water demand pattern
 A better estimate of storage requirement can be made
using the mass curve technique based on
rainfall and
water demand pattern.

Cumulative rainfall runoff and cumulative water
demand in year is calculated and plotted on the
curve.

same
The sum of the maximum differences, on the either
side, between the rainfall curve and water demand
curve gives the size of the storage required
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Storage capacity
Example 2:
Calculate the size of the storage tank required for a school
with 65 students and 5 staff, assuming average water
consumption of 5 litres/day.
Roof area = 200 m2.
Assume runoff coefficient of 0.9.
The rainfall pattern in the area is given in the table below
Average daily demand = 70 x 5 = 350 litres
Yearly demand = 350 * 365 = 127750 litres = 127.75 m3
Average monthly demand = 127.75/12 ~ 10.65 m3
57
Storage capacity calculations
(a) Rainfall pattern - 1
Month
Rainfall
150
Jan
Feb
Mar
Apr
May
June
July
Aug
Sep
Oct
Nov
Dec
120
90
70
120
40
50
45
15
Rainfall (mm)
mm
100
50
0
45
70
45
J
F
M
A
M
J
J
Month
58
A
S
O
N
D
Calculation of required storage capacity (1)
Month Rainfall Rainfall
Water
Cum. Rainfall Cum. Water Difference
harvested Demand harvested CH Demand CD CH - CD
m3
m3
m3
m3
m3
mm
J
120
21.6
10.65
21.6
10.65
10.95
F
90
16.2
10.65
37.8
21.3
16.5
M
70
12.6
10.65
50.4
31.95
18.45
A
120
21.6
10.65
72
42.6
29.4
M
40
7.2
10.65
79.2
53.25
25.95
J
50
9
10.65
88.2
63.9
24.3
J
45
8.1
10.65
96.3
74.55
21.75
A
15
2.7
10.65
99
85.2
13.8
S
0
10.65
99
95.85
3.15
O
45
8.1
10.65
107.1
106.5
0.6
N
70
12.6
10.65
119.7
117.15
2.55
D
45
8.1
10.65
127.8
127.8
0
Required storage capacity = 29.4 m3 say 30 m3
59
Mass curve for calculation of required
storage capacity
Cum. Demand
Cum. Harvested
140
120
Water (m3)
100
80
60
40
20
0
J
F
M
A
M
J
J
Month
60
A
S
O
N
D
Mass curve for calculation of required
storage capacity
140
3
Cumulative (m )
120
Harvested
Water demand
100
80
60
40
20
0
J
F
M
A
M
J
J
Month
61
A
S
O
N
D
Storage capacity calculations
(b) Rainfall pattern - 2
Month
Rainfall
mm
120
100
100
115
120
Rainfall (mm)
Jan
Feb
Mar
Apr
May
June
July
Aug
Sep
Oct
Nov
Dec
140
100
80
60
40
20
0
55
100
120
J
F
M
A
M
J
J
Months
62
A
S
O
N
D
Calculation of required storage capacity (2)
Month Rainfall
mm
J
F
M
A
M
J
J
A
S
O
N
D
120
100
100
115
0
55
100
120
Rainfall
Water
Cum. Rainfall Cum. Water Difference
harvested Demand harvested CH Demand CD CH - CD
m3
m3
m3
m3
m3
21.6
10.65
21.6
10.65
10.95
18
10.65
39.6
21.3
18.3
18
10.65
57.6
31.95
25.65
20.7
10.65
78.3
42.6
35.7
0
10.65
78.3
53.25
25.05
0
10.65
78.3
63.9
14.4
0
10.65
78.3
74.55
3.75
0
10.65
78.3
85.2
-6.9
0
10.65
78.3
95.85
-17.55
9.9
10.65
88.2
106.5
-18.3
18
10.65
106.2
117.15
-10.95
21.6
10.65
127.8
127.8
0
Required storage capacity = 35.7 + 18.3 = 54 m3
63
Gutters
 Gutters are channels all around the edge of a sloping
roof to collect and transport rainwater to the storage
tank.
 A carefully designed and constructed gutter system
essential for any roof catchment system to operate
effectively.
 When the gutters are too small considerable
quantities of runoff may be lost due to overflow during
storms.
 The size of the gutter should be according to the flow
during the highest intensity rain. It is advisable to
make them 10 to 15 per cent oversize.
64
is
Gutters (2)
 A general rule of thumb is that 1 cm2 of guttering is
required for every m2 of roof area.
 Gutters can be semi-circular or rectangular and could
made using a variety of materials:
Locally available material such as plain galvanised
iron sheet (20 to 22 gauge), folded to required
shapes.
-
Semi-circular gutters of PVC material can be
readily prepared by cutting those pipes into two
equal semi-circular channels.
-
Bamboo or betel trunks cut vertically in half.
-
Wood or plastic
65
be
Gutters (3)
 Gutters need to be supported so they do not sag or fall off
when loaded with water.
 The way in which gutters are fixed depends on the
construction of the house;
it is possible to fix iron or timber brackets into the
walls, but for houses having wider eaves, some
method of attachment to the rafters is necessary.
 A properly fitted and maintained gutter-downpipe
system is capable of diverting more than 80% of all
runoff into the storage tank, the remainder being lost
through evaporation, leakage, rain splash and overflow.
66
Gutters - Shapes and Configurations
Gutter configurations
67
Gutters - Shapes and Configurations
68
Gutters and Hangers
69
Shade cloth guttering
Source: Peter Morgan (1998)
http://aquamor.tripod.com/RAINWATER.htm
70
Plastic sheet guttering
http://www.eng.warwick.ac.uk/DTU/pubs/wp/wp55/8gutter.html
71
72
Gutter sizing
Recommended gutter widths for use in humid tropics
Gutter width (mm)
Roof area (m2) served by 1
gutter
55
13
60
17
65
21
70
25
75
29
80
34
85
40
90
46
95
54
100
66
Source: (Still and 73
Thomas, 2002)
Gutter sizing
Optimum roof area drainable by square gutters (considering
only conveyance)
Square
gutters
Slope (%)
0.5
Gutter
width
1
2
4
Optimum roof area served by gutter (m2)
33 mm
10
14
20
28
50 mm
29
42
60
85
75 mm
88
125
177
250
100 mm
190
269
380
538
Source: (Still and 74
Thomas, 2002)
Guttering for a 60 m2 roof
Square
0.5% slope
Square
1% slope
Half round
1.0% slope
45o Triangle
1.0% slope
Material use
(mm)
214
189
150
175
Gutter width
at top (mm)
71
63
96
124
Cross
sectional area
(cm2)
47
39
36
38
Source: http://www.eng.warwick.ac.uk/DTU/rwh
75
Guide to sizing of gutters and downpipes for
rainwater harvesting systems in tropical regions
Source: www.sopac.org
Roof area (m2)
served by one gutter
Gutter width
(mm)
Minimum diameter
of downpipe (mm)
17
60
40
25
70
50
34
80
50
46
90
63
66
100
63
128
125
75
208
150
90
76
First flush system (1)

Debris, dirt, dust and droppings will collect on the
roof of a building or other collection area.

When the first rains arrive, this unwanted matter will
be washed into the tank. This will cause
contamination of the water and the quality will be
deteriorated.

Many RWH systems therefore incorporate a system
for diverting this ‘first flush’ or ‘foul flush” water so
that it does not enter the storage tank.

Several first flush system are in use. The simplest
one is a manually operated arrangement whereby
the inlet pipe is moved away from the tank inlet and
then replaced again once the initial first flush has
been diverted.
77
First flush system (2)

For an average roof catchment it is suggested that
the first 20–25 L could be diverted or discarded.

First flush devices should be regarded as an
additional barrier to reduce contamination and should
not be used to replace normal maintenance activities
designed to keep roof catchments reasonably clean.

The inlet pipe to all rainwater tanks should be easily
detachable so that, when necessary, the tank can be
bypassed. Manual detachment could be used as an
alternative to an engineered first flush device, although
the level of control will not be as good.
78
First flush system (3)
Developed by Khon Kaen
University, Thailand
79
First flush system (4)
80
First flush system (5)
81
First flush
system (6)
82
Device for separating rainwater from roofaccumulated impurities
83
Roof catchment system with filter and
storage tank
84
Storage tank & first flush - Malaysia
85
Part 4
QUALITY ASPECTS OF RWH
86
Quality of Rainwater (1)

The quality of rainwater is relatively good but it is
not free from all impurities.

Analysis of stored rainwater has shown some
bacteriological contamination.

The rainwater is essentially lacking in minerals,
the presence of which is considered essential in
appropriate proportions.

Cleanliness of roof and storage tank is critical in
maintaining good quality of rainwater.

The storage tank requires cleaning and
disinfection when the tank is empty or at least
once in a year.
87
Quality of Rainwater (2)
 The extraction system (e.g. taps/faucets, pumps) must
not contaminate the stored water.
 The first run off from the roof should be discarded to
prevent entry of impurities from the roof.
 Some devices and good practices have been suggested
to store or divert the first foul flush away from the storage
tank.
 In case of difficulties in the rejection of first flow, cleaning
of the roof and gutter at the beginning of the rainy season
and their regular maintenance are very important to
ensure better quality of rainwater.
88
Quality of Rainwater - Bacteriological
 Dust from the soil, and droppings of birds and animals
could be the source of contamination by the bacteria.
 When first flush eliminating devices are absent, all the
indicator bacteria are generally present in water samples in
numbers beyond what is acceptable by any standards.
 Tree hanging in the vicinity, definitely enhances the
possibility of contamination due to increased access of the
roof to birds and animals. Also leaves contribute to organic
loading of the water samples, which in turn act as nutrient for
bacterial growth.
89
Disinfecting rainwater
• Rainwater is generally of very good chemical quality. However, it
may not meet WHO drinking water quality standards, specifically
microbiological quality standards, hence some disinfection is
recommended.
• Rainwater can be used for drinking, if it is clear, has no or very
little taste or smell and is from well maintained system.
• Disinfection can be done by:
• boiling the water in before consumption
• adding chlorine compounds/bleaching powder in required quantity
to the water stored in the tank
• using slow sand filtration
• solar disinfection (SODIS)
90
Disinfecting rainwater (2)

For disinfection using bleaching powder, the general
dosage recommended is 10 mg of bleaching powder
containing 25% of free chlorine per litre of water. This
meets the required standard of 2.5 mg of chlorine per litre
of water.

After adding the bleaching powder, the water should be
stirred thoroughly for even distribution of the
disinfectant
agent. The water should be kept without
use for about 30
minutes after adding bleaching
powder.
91
Operation and maintenance

The simple operation and maintenance of RWH
systems is one of the most attractive aspects of the
technology.

The extent of maintenance required by a basic
privately owned household RWH system includes
- Regular cleaning of the roof tops and gutters
- Frequent cleaning of storage tanks
- Inspection of gutters and feeder pipes and valve
chambers to detect and repair leaks

When ground catchment is used for collection and/or
ground tank is used for storage, proper fencing of
both
is recommended to keep the children and animals away, thus
avoiding contamination and risks
of falling into the tank.
92
93
One example of a flat screen
over the gutter to keep large
debris out of the tank.
A problem with gutter screens is
that they require a lot of
maintenance to keep leaves and
debris from piling up and
blocking the screens.
Also, dirt on the leaves can still
be washed into the storage tank.
Source: Guidelines on Rainwater
Catchment Systems for Hawaii
94
Leaf Eater®/Leaf Beater®/Leaf Catcha®
Source: http://www.rainharvesting.com.au
95
Tank desludging and cleaning (1)
 Accumulated sediments can be a source of chemical
contamination and off-tastes and odours. All tanks should be
examined for accumulation of sediments every 2–3 years.
 Sludge can be removed by siphoning without emptying the
tank. Sludge may also be pumped from the tank with
minimum loss of water by using a suitable motor-operated pump
and attachments.
 Sludge can also be removed by draining and cleaning the tank. If
a drain plug is provided at the base of the tank, water can be run to
waste to discharge the sludge. Once the tank is empty, the
remaining sludge can be scooped up and
removed through the
access opening.
96
Tank desludging and cleaning (2)
 It is important to check the structural condition of the tank before
choosing a method of cleaning.
 Cleaning should generally be limited to removing accumulated
sediments, leaf litter etc. Harsh (chemical) cleaning methods may
accelerate deterioration, for example, removing the protective layer
on the inside walls of a steel tank will lead to tank corrosion.
 After cleaning, it is recommended that the internal walls and floor
of the tank be rinsed with clean water. Rinse water and sediment
should be run to waste.
 Where cleaning necessitates entering the tank, take care to
ensure adequate ventilation is provided and an additional person is
in attendance.
97
The Thai Rainwater Jar Programme
 Nationwide rainwater harvesting programme which dramatically
improved the rural water supply coverage, especially in North eastern
Thailand
• 10 million rainwater jars constructed in 5 years
(1985-1990).
 Factors favouring rapid development RWH programme
• a real felt need for water
• a preference for the taste of rainwater
• the availability of cheap cement and skilled artisans
• a pool of indigenous engineers, technicians and administrators
committed to rural development programme
98
Thai Jar
Khon Kaen, Thailand
Source: http://www.ircsa.org
99
Rainwater Harvesting - Australia
More than one million
people in Australia rely on
rainwater as their primary
source of water supply
100
Rainwater Harvesting - Australia

In Australia the use of domestic rainwater tanks is an
established and relatively common practice, particularly in rural
and remote areas.

Between 1994 and 2001, 16% of Australian households
used rainwater tanks, with 13% of households using tanks as
their main source of drinking water.

7% of the capital city households and 34% of non-capital
city households have rainwater tanks.

In a 1996 South Australian survey, 28% of Adelaide
households used rainwater tanks as the primary source of
drinking water compared to 82% households in the rest of the
State.
Source: Guidance on use of rainwater tank. En Health, Australian Government 2004
101
102
Rainwater
harvesting system,
in Patan,
Nepal
1 - Overhead tank
2 - Downtake PVC pipe from roof
3 - First phase storage drum
4 - Overflow goes into
underwater tank
5 - Pump to lift water to overhead
tank
6 - Sediment discharge tap
7 - 50,000 litre underground
ferrocement tank
103
Source: Nepali Times (16-22 August 2002)
Rainwater Harvesting in Tokyo
104
Rainwater Harvesting from Domed Stadium
in Japan
105
Source: Zaizen et al. (1999)
Rainwater Harvesting from Domed Stadium
in Japan
_________________________________________________________
Stadium
Tokyo
Fukuoka
Nagoya
_________________________________________________________
Catchment area
for storage (m2)
16,000
25,900
35,000
Capacity of
detention tank (m3)
1000
Utilization
Flush toilets
1800
1500
Flush toilets,
Flush toilets
watering plants
watering plants
__________________________________________________________
Source: Zaizen et al. (1999)
106
Rainwater Harvesting at Changi Airport Singapore

Rainfall from the runways and the surrounding green
areas is diverted to two impounding reservoirs.

One of the reservoirs is designed to balance the flows
during the coincident high runoffs and incoming tides, and the
other reservoir is used to collect the runoff.

The water is used primarily for non-potable functions such
as fire-fighting drills and toilet flushing.

Such collected and treated water accounts for 28 to 33%
of the total water used, resulting in savings of approximately
S$ 390,000 per annum.
107
Rainwater Harvesting in Presidential Estate,
New Delhi, India
-
About 7000 residing in the estate and about 3000 visitors
every day. There is also famous “The Mughal Garden”.
Total water demand 2 million litres per day
30% of demand met by Groundwater wells in the estate and
groundwater level is going down
108 rapidly)
Rainwater Harvesting in Presidential Estate,
New Delhi, India
 Rainwater from the northern side of the roof and
paved areas surrounding the presidential palace is
diverted to an underground storage tank of 100,000
litres capacity for low quality use (5%).
 Overflow the rainwater storage tank is diverted to
two dug wells for recharging.
 Rainwater from southern side of the roof is diverted
for recharging a dry open well. Rainfall runoff from
the staff residential area is also diverted to dry wells.
 15 m deep recharge shafts have been constructed
for recharging.
109
Water Supply at Millennium Dome, London
 Water Supply Plant, installed at the UK's Millennium Dome
can supply around 500 m3 per day of reclaimed water to flush
all of the toilets and urinals on the site.
 Water is reclaimed from greywater produced by the hand
wash basins, rainwater from the dome's roof, and groundwater
from the chalk aquifer which is located below the site.
110
Water Supply at Millennium Dome, London



Rainwater is collected from dome roof and adjacent
areas (100,000 m2)
Size of collection tank is 800 m3
Reed beds are used for treatment
111
Socio-cultural Considerations (1)

The success of any rain water harvesting system or
programme ultimately depends on the interest,
enthusiasm and active support of the user community for
the technology.

RWH system, even if technically appropriate and
justified based water resources condition, it is not
likely to be successful if it is socially unacceptable or
inappropriate in anyway.

Local customs, perceptions and preferences must be
given high priority when considering the feasibility of the
technology and possible implementation
strategies.
112
Socio-cultural Considerations (2)

It is always vital to be sensitive to local perceptions
regarding quality and suitability of rainwater.

Although some people regard rainwater as sweet and
tasty (especially those used to drinking somewhat
saline groundwater), others consider it to be flat and
tasteless (particularly when compared to water with high
mineral content).

Local customs, perceptions and preferences must be
given high priority when considering the feasibility of the
technology and possible implementation strategies.
113
Public Awareness and Demonstration

Public awareness and education are essential in order
to improve acceptance of rainwater collection and
utilisation.

Efforts should be made to change public perception of
rainwater from being viewed as a nuisance to being
viewed as an asset.

Demonstration projects are key for improving public
acceptance and assisting in the removal of institutional
barriers.

To promote rainwater utilisation, basic policies,
implementation strategies, technology development and
networking are required.
114
115
Bibliography

Rainwater Harvesting and Utilization. An Environmentally Sound
Approach for Sustainable Urban Water Management: An Introductory
Guide for Decision-Makers. IETC-UNEP, Japan.

Rainwater catchment systems for Household Water Supply
(1991). Environmental Sanitation Reviews No No 32. ENSIC,
Bangkok, Thailand.

UNEP-IETC (1999) Proceedings of the International Symposium on
Efficient Water Use in Urban Areas - Innovative Ways of Finding Water for
Cities. (8 to 10 June 1999), Kobe, Japan.

Gould, J. and Nissen-Petersen, E. (1999) Rainwater Catchment
Systems for Domestic Supply. IT Publications, London

Hasse, R. (1989) Rainwater Reservoirs- Above Ground Structures for
Roof Catchment. GTZ.

NGO Forum and SDC (2001) Rain Water Harvesting System. NGO
Forum for Drinking Water Supply and Sanitation and SDC,
116
Bangladesh.
Web Resources on RWH

International Rainwater Catchment Systems Association
http://www.eng.warwick.ac.uk/ircsa/

American Rainwater Catchment Association
http://www.arcsa-usa.org/

Centre for Science and Environment (CSE), India
http://www.rainwaterharvesting.org

Development Technology Unit, School of Engineering,
University of Warwick, UK
http://www.eng.warwick.ac.uk/DTU/rwh/index.html

Chennai Metrowater, India
http://www.chennaimetrowater.com/rainwaterfaqs.htm

Rainwater Partnership
http://www.rainwaterpartnership.org/
117
Web Resources on RWH (2)

Lanka Rainwater Harvesting Forum
http://www.rainwaterharvesting.com

Intenational Rainwater Harvesting Alliance
http://www.irha-h2o.org/

Greater Horn of Africa Rainwater Partnership (GHARP)
http://www.gharainwater.org/

The Web of Rain
http://www.gdrc.org/uem/water/rainwater/rain-web.html
118