India; Rainwater Harvesting Made Simple - Friends of Paradise

1. Rainwater Harvesting
Made Simple

2. Rainwater Harvesting Made Simple
WHAT IS RAINWATER HARVESTING?
Rainwater harvesting is essentially the capture of rainwater when it rains. This
water can be stored and re-used, or can be recharged into the ground.
Water is essential to all life forms on earth - human, animal and vegetation. It is
therefore important that adequate supplies of water be developed to sustain such
life. Development of water supplies should, however, be undertaken in such a way
as to preserve the hydrological balance and the biological functions of our
ecosystems.
As land pressure rises, cities are growing vertical and in countryside more forest
areas are encroached and being used for agriculture. In India the small farmers
depend on Monsoon where rainfall is from June to October and much of the
precious water is soon lost as surface runoff. Hence, it is important to conserve, re-
use (in case of rainwater) and recycle (in case of wastewater) water to ensure that
this important resource essential to life is not depleted.
'Rain Water Harvesting' (RWH), a technique that has been used in India for many
centuries, is now gaining importance as a supplemental source of water. Water
harvesting is essentially the activity of collection of rainwater, which can be stored
for direct use or can be recharged into the groundwater.

3. NEED FOR RAINWATER HARVESTING:
 As water is becoming scarce, it is the need of the day to attain self-
sufficiency to fulfill the water needs.
 As urban water supply system is under tremendous pressure for supplying
water to an ever increasing population.
 Groundwater is getting depleted and polluted due to excessive use.
 Soil erosion resulting from the unchecked runoff.
 Health hazards due to consumption of polluted water.
 More concrete and roads – lesser percolation of rainwater naturally unlike
olden days.
 Surface water bodies like lakes being destroyed due to unscrupulous
development.
Status in Bangalore:
 No perennial source of water near the city
 Lakes were the only source of water to the city
 Status of lakes:
o 1960 – 262 lakes in the green belt area
o 1986 – 127 left, only 81 alive
o 2009 – 17 good lakes1 currently present
1
http://en.wikipedia.org/wiki/Lakes_in_Bangalore accessed 2010

4.  This is due to Encroachment and Eutrophication (excess nitrate in the lake
causing growth of algae and plankton)
 Arkavathi River has minimal supply
 Currently, water supply is from the Cauvery river, which is located 510mts
below Bangalore and 100 kms away
 The cost of pumping water alone is Rs 16 – Rs 18/Kl
 Taking into account the cost of distribution and transportation across the
city, BWSSB spends about Rs. 40 /Kl
 However, domestic customers are charged only Rs 6/Kl
 Even after pumping Cauvery water, the shortfall of water in the city was
495MLD in 2001
 Majority of the population depends on groundwater. Unsustainable use of
ground water has resulted in a drop in the water table of 5.4 mts in 18 years
BENEFITS OF RAINWATER HARVESTING:
1. Environment friendly and easy approach for water requirements
2. RWH is the ideal solution for all water requirements.
3. Increase in ground water level.
4. Mitigates the effects of drought.
5. Reduces the runoff, which otherwise flood storm water drains.
6. Reduces flooding of roads and low-lying areas.
7. Reduced soil erosion.
8. Improves the ground water quality, since rainwater is largely free from
minerals, bacteria and other contaminants..
9. Low cost and easy to maintain.
10. Reduces water and electricity bills.
WHO CAN HARVEST RAINWATER?
 Rainwater harvesting is for any person planning to build a house or who is
in the process of building a house on an independent plot.
 It makes ecological and financial sense not to waste a pure natural resource
available in large quantity on one’s roof.
 In the case of a homebuilder, at an initial stage of construction, investments
in time, design and money are minimal for adopting roof rainwater
harvesting.2
HOW MUCH WATER CAN I HARVEST IN MY HOME?
2
http://www.rainwaterclub.org/index.htm accessed August 2009

5. Bangalore receives about 970mm each year. This is spread across 6-8 months. Based
on
the plot size and rooftop we can calculate the harvestable rainfall endowment for
each
home. The table below illustrates the water that is available for rooftop harvesting:3
Plot size Rooftop Water harvested Value in Rs of water harvested
(sqft) (sqm) ~ 75% annually for 970mm annually (at current tanker water
of plot size of rain (litres) rates for Rs 50/- per 1000 litres)
1200 83 72,000 3,607
2400 165 1,44,000 7,214
4000 275 2,40,000 12,024
5000 344 3,01,000 15,030
In Ferns Paradise, the average monthly usage of water per household is 60kl (using
monthly water meter data). This amounts to 720kl of water per household on an
annual basis.
Based upon the above calculation, this means that the water harvested will be
sufficient for 150 days (even at 2000 litres per day).
Alternatively, the rainwater can be used for re-charging the groundwater which
will improve the ground water table (level as well as quality of water) over a period
of time.
WHAT CAN I USE MY RAINWATER FOR?
The rainwater thus collected can be used for most household purposes, like
cleaning, gardening, flushing, laundary, car washing etc.
BASIC ELEMENTS OF A RAINWATER HARVESTING SYSTEM
Irrespective of complexity, rainwater-harvesting systems have three basic
components.
1 Catchment : The surface from which rainwater is collected for storage. This could
be a rooftop, a paved flooring surface, or a landscaped area. Catchment area is the
area of that surface, usually calculated in m2 (square metres).
3
Calculation done by Biome Environmental Solutions Pvt. Ltd

6. 2 Conveyance: They lead the water from the catchment surface to the storage tank.
For rooftops rainwater gutters and rainwater down pipes are conveyance systems,
which need to be designed appropriately so as to manage the severest intensity of
rain as well as not to lose any water during the conveyance process. Storm water
drains, French drains with pebbles are also conveyance systems.
3 Storage tanks: From the simplest ground level tank, to underground sumps,
surface lined ponds and large lakes storage options are many depending on the
context of the rainwater harvesting design. These can be above or below the
ground. In some cases, the soil profile may also permit artificial recharge of
rainwater to open wells and borewells where water can be stored to be retrieved
later for productive use.
HOW DO I DESIGN A ROOFTOP RAINWATER HARVESTING SYSTEM FOR MY HOUSE?
Step 1: Calculate the quantity of water
Calculate the rooftop area – both the flat as well as the sloped areas. The area
should be in m2
Calculate the total amount of water that can be harvested.
Water harvested (l) = catchment area (m2) * runoff coefficient (0.8) * annual rainfall
(mm)
Runoff coefficient is the natural loss of water when flowing on a surface. For a
concrete surface, the coefficient is 0.8.
So, if the rooftop area = 1500 sq ft. = 140 sq.m. , the amount of water that can be
harvested annually in Bangalore can be calculated as:
Amt of water = 140*0.8*900 = 1,00,800 litres
Step 2: Designing the roof area
Some tips to design your roof top area to efficiently capture rainwater.
 A flat roof can be gently sloped to drain water towards the downtake pipes.
Ideally, it should be designed so that the slope is towards one side, so as to
prevent the need for too many downtake pipes. A 'nahani trap' or 'floor trap'
can be placed at the time of casting the roof just near the inlets of the downtake
pipes

7.  Sloping roofs should have a gutter of PVC or zinc sheet to collect water &
channel it to the down water pipe system.
 Roofs should be uncluttered & should be easy to clean by sweeping &
swopping if necessary.
Gutters to collect water from sloped roofs
It is important to keep the roof are clean so as to ensure that the rainwater collected
is free from dust and bacterial contamination.
Step 3: Downtake pipes
90mm dia. PVC pipes resistant to UV rays appear to be the best option for
downwater pipes. Of course, this depends upon the roof area to be drained. The
number of downtake pipes that will be required depends upon the area to be
drained. About 3 to 4 downwater pipes seem sufficient for 1000 to 1200 sft area.
These can be connected to each other either to form one or two outlets to lead to the
storage system.
Step 4: Filter
It is important to filter the water before it enters the storage tank so as to remove
the dirt and other particles. Filtering can be as basic as a floor trap placed before the
water enters the downwater pipe or a piece of sponge placed at the inlet of the
downwater pipe. However, a PVC bucket with gravel, sand & charcoal is a good
filter before rainwater is stored. A small two chamber inspection/ filter tank can
also be devised
There are different types of filters in the market. Details of these filters are available
in the Annexure.

8. Step 5: First flush diverter
The first rain that falls after a long dry spell usually carries down with it a lot of
dirt, dust, and debris that would have collected over the roof. It also dissolves
many air pollutants on its way down. It is, therefore, a safe practice to divert the
first run-off away from the storage tank for which a first-flush diverter is used.
After the ‘first-flush’, water that is collected is cleaner.
There are different types of first-flush diverters but most are not commercially
available in India and Karnataka. The RAINY filter and the pop-up filter (see
Annexure) also act as first-flush diverters, but if these filters are not used then one
would have to fashion a first-flush diverter themselves.
One that is relatively easy to build and maintain is the standpipe. The standpipe
consists of a vertical PVC pipe perpendicular to the pipe that leads into the storage
tank. It has a threaded plug at the bottom. Water from the downtake pipe fills up
the standpipe and when full, water is allowed to go into the storage tank. The
threaded portion at the bottom must be removed after each rainfall to drain out the
water in the standpipe and keep it empty for the next rainfall.
Step 6: Storage/Recharge
Rainwater that is harvested can either be stored or can be used to recharge the
groundwater. The ideal system would a combination of both – a storage tank,
with an overflow pipe connected to a recharge well.
Storage Tank
A storage tank could be:
 A roof-level storage tank
 Ground level drum or masonry tank
 Below the ground sump
During the construction phase, it is most practical to opt for an underground
storage tank, since it is easier to design and will work out to be less expensive.
Some points to keep in mind are:
 Roof level storage tanks may need to be at the rear of the house or on the
sides so that it is neither obtrusive nor visually offensive.
 Ground level drums or tanks occupy space and should not hinder
movement or appear unsightly.
 Below the ground sump is a good option since most new constructions in
Bangalore go in for sumps anyway. Sumps are hidden from view, less costly
to build and do not obstruct movement.

9. Note: always provide for an overflow pipe for excess collection of water from the
storage system
The size of the storage tank would depend primarily on the space available. If we
assume an average daily rainfall of 30 mm, then the amount of rainwater that can
be collected from a catchment area of 140 sq m will be 3360 litres. Typically, the size
of the storage tank can vary from 3000 to 6000 litres.
Recharge Well
A recharge well is used to recharge the groundwater. While it does not directly
reach the water table, a recharge well is a good way to moisturize the soil and let
water seep its way to the water table. Infiltration through the soil also helps in
filtering out the impurities in the water.
A recharge well is typically 25 – 30 ft deep, and can be of a 3’ to 8’ diameter,
depending on the quantity of water as well as space and budget. It is lined with
concrete rings, but the bottom of the well is unlined. Rainwater fills the well and
slowly infiltrates into the ground. It typically takes about 3- 4 hours for the water to
completely seep into the ground.
WHAT IS RECOMMENDED IN FERNS PARADISE?
Since Ferns Paradise is entirely dependent upon borewells for its water
requirement, it makes both environmental and economic sense to recharge our
groundwater. While proposals are being evaluated to implement a community
rainwater harvesting system, we would like to recommend that every house
implements a rainwater harvesting system with groundwater recharge.
Constructing a storage system would help in re-using the water for various uses
such as landscape.
To work towards the common goal of enhancing our water sources for the future
generation, we recommend all new constructions to have a storage tank (for
immediate re-use), with an overflow pipe leading to a recharge well.
CASE STUDIES
Case Study 1 – Construction phase with storage option

10. Plot size: 50ft by 100 ft
Roof area: Approximately 1500 sqft.
Since the plan for rainwater harvesting was conceived during the construction
stage, the owners decided to build a rainwater harvesting (RWH) tank which was
separate from the drinking water sump. The capacity of the RWH tank is 6000
litres. It is an underground tank and is located at the back of the house. The tank is
lined with 5’ diameter cement rings. The tank is fitted with a 3-layer filter of gravel,
sand and activated carbon, at the top.
There are 5 downtake pipes – 3 coming down from the left side of the house and 2
from the right side. In each side, the downtake pipes are joined underground so
that there are 2 pipes finally entering the tank. The water entering the RWH tank
passes through the filter before being stored in the tank. There is a self-priming
pump that is used to pump water from the tank. A gate valve is used to divert the
water either for gardening or to the overhead tank.
There are 2 overhead Syntex tanks, each of 1000 litre capacity. One tank is
connected to all the bathrooms, and the other is connected only to the kitchen. The
connecting pipe between the tanks has a gate valve.
The water in the RWH tank can be used both for gardening as well as in the
bathrooms. Since there is a basic level of treatment, the water is perfect to use in
bathrooms. If it has to be used for drinking, then additional treatment for bacterial
contamination is necessary. However, the owners did not want to use the water for
drinking purposes.
The total cost of the tank and the filter was Rs. 10,000/-
By using rainwater, the consumption of supplied water has dropped by 10-20 kl
during the rainy season.
Case Study 2 – Construction phase with storage plus recharge option
Plot size: 10000 sq ft
Roof area: approx 3000 sq ft
The rainwater harvesting system was implemented during construction. Hence the
roof was sloped so as to collect the rainwater in five downtake pipes. Each
downtake pipe has a filter to remove the grit and leaves, and they are all connected

11. to an underground sump (separate from the drinking water sump). The capacity of
the sump is 8000 Litres.
The overflow pipe from this sump is connected to a recharge well, which is 5’
diameter and 25’ deep. It is lined by concrete rings, and the bottom is unlined. A
first flush diverter is present before the water enters the sump. 2 mm of rainfall is
collected in the pipe and this is diverted directly to the recharge well, hence the
storage tank is kept clean.
A valve has been installed so as to allow by-pass of the storage tank, and enable all
the rainwater to go into the recharge well.
Rainwater harvested = approx. 240,000 litres annually
Case Study 3 - Retrofit4
ROOF: The roof area is approximately 650 square feet. The roof was given a slope
to bring all the rainwater to one point. The rainwater is brought down through one
90 mm diameter down-pipe to a first rain separator.
When the terrace is being cleaned, the cap of the first rain separator can be opened
and the dirty water allowed to flow in to the front garden. After cleaning the cap is
closed and the first rain separator collects the first 1.50 mm of rain falling on the
terrace every time it rains. The maximum amount of silt and dust on the roof is
picked up in this vertical pipe first rain separator leaving cleaner rainwater to be
filtered and stored for use.
FILTER: Then the rainwater is filtered using a 90 litre blue colored HDPE drum.
Rainwater enters from below the drum and passes through two layers of sponge
kept at intervals. The water is then picked up at the top and led into the sump tank
of capacity 6000 litres.
During heavy rains if the sump tank fills up, the overflow of rainwater is led into
an open well on site. The house is a ‘zero runoff’ house in so far as rainwater is
concerned. All rainwater falling on the plot or the roof is either collected or allowed
to recharge into the open well. In fact the side setback area is left unpaved to allow
for infiltration of rainwater too.
Rainwater available = 82,080 litres
Rainwater harvested = 65,664 litres
4
http://www.rainwaterclub.org/domestic_prithvi.htm accessed August 2009

12. CONTACTS
Below is a list of organizations that design and implement rainwater harvesting
systems in Bangalore:
1. Biome Environmental Solutions Pvt. Ltd
Contact persons: Shubha or Avinash
1022, 6th Block, 1st Floor, HMT Layout
Vidyaranyapura Main Road
Vidyaranyapura, Bangalore – 560 097
INDIA
Phone: 91-80-41672790
Email: contact@biome-solutions.com
Website: http://www.biome-solutions.com/
2. Farmland Rainwater Harvesting:
Contact persons: Vijayraj or Michael
648, 11th Cross, 7th Block, Jayanagar
Bangalore - 560 082
Ph : 94481 30524, 94480 76595
Telefax: 080 - 2676 6252
e-mail : farmland_rhs@yahoo.co.in
website : www.rainwaterharvestingindia.com
www.rainyfilters.com
3. Karnataka State Council for Science and Technology
Contact person: A. R. Shivakumar
Indian Institute of Science, Bangalore - 560 012
Phone : 080 23341652
TeleFax : 23344880
E-mail : rwhkscst@vsnl.net / rainmanskumar@yahoo.com
Website: http://kscst.org.in/rwh.html
4. Rainwater Club
Contact person: S. Vishwanath,
1022, 6th Block, 1st Floor, HMT Layout, Vidyaranyapura Main Road,
Vidyaranyapura, Bangalore - 560 097 India
Phone: 91-80-41672790
Email: rainwaterclub@gmail.com
Website: http://www.rainwaterclub.org/

13. Annexure - Details on Filters
There are several filters available in the market and can also be made at home. The
list provided is not meant to be exhaustive – it is only an indication of some of the
filters that are available.
Option 1 - Varun
Varun is a slowsand filter constructed in a 90-litre (HDPE) drum. The lid is turned
over and holes are punched in it. This is the first
sieve which keeps out large leaves and twigs.
Rainwater then passes through three layers of
sponge and a 150-mm thick layer of coarse sand.
The filter removes suspended particles from the
harvested rainwater. Varun has been developed by
S Vishwanath, a Bangalore-based water-harvesting
expert. According to him, ‘Varun’ can handle a 50-
mm-per-hour intensity rainfall from a 50-m2
(square metre) roof area on a decently clean roof. Based on these calculations, when
a rainwater-harvesting system is being designed for a new house, the optimal
number of filters can be recommended.
Maintenance The sponge needs to be cleaned periodically, and the top layer of sand
to a depth of about 3 cm needs to be cleaned at the end of a rainy season. Sponge
can be removed and soaked/cleaned in a bucket of water and replaced. Sponges can
have fungal growth if prescribed maintenance is not followed. If charcoal is used, it
must be changed every year. It is also advised to clean the meshes and the top layer
of gravel.
Cost A filter that can service a rooftop area of 100 m2 costs about Rs 4500 (Price in
Bangalore in 2006).
Option 2 – RAINY filter
A product made by Farmland Rainwater
Harvesting Systems Ltd, this wall-mounted filter
is designed to be inserted directly into the vertical
section of rainwater downtake pipes. It consists
of a very fine (0.20 mm) SS-304 steel mesh which
is housed in a HDPE casing. It works on the
cohesive force principle. As the water passes
through the filter, silt, insects, and debris
continue to move down the pipe into a drain,

14. while clean water flows outwards through the mesh into a pipe that is
perpendicular to the inlet pipe. The filter is stated to have an efficiency of 85%. Two
models of RAINY, suitable for different roof areas are available. Model FL-150 is
suitable for roof areas up to 110 m2 (square metre) and Model FL-250 for roof areas
up to 230 m2. The patent for this filter has been applied for.
Maintenance: This is a relatively maintenance-free filter, since there is automatic
flushing during heavy rains. If required the mesh can be removed and washed to
eliminate the suspended particles blocked inside. This can be done after the rainy
season.
Cost (Prices in Bangalore in 2006): Model FL-150 costs Rs 4750 and Model FL-250
costs Rs 8750
Option 3 – Ground filter
Water collected from the rain water pipe. It passes through this
filter at Ground level and then flows to the sump tank. It has a
valve to divert the first rain collected to ground or the drain. The
filter is multilayer
fibre mesh. They are
available in 3” and 4”
sizes. If the
catchment area is
more than 700 sq ft, a
4” size would be
preferable.
Maintenance: The mesh will need to be
taken out periodically after 4 – 5
rains.
Contact person: Mr. Venkatesh -
9980522434