This presentation provides a quick look at the basics of domestic rainwater harvesting and grey water recycling.

1. RAINWATER HARVESTING AND GREYWATER RECYCLING
IN URBAN AREAS – THE CHENNAI EXPERIENCE
Seetha Gopalakrishnan
India Water Portal

2. Rainwater Harvesting - Basics
Is this a novel concept?
 Not a new technology or an alternative
 Adaptations - Traditional vs. Modern designs
Why should I harvest rainwater?
 No. of rainy days are less – around 60-90 days on an average across India
 Cities are usually water starved, not rain starved
 Needs - Immediate use vs. Groundwater recharge
Is it expensive?
 Not very if it is incorporated in the original design
How do I go about this?
 Harvest rainwater, both from the roof-top as well as around the building – Simple design

3. Rooftop Rainwater Harvesting

Terrace down-take pipes → Underground sump │Overflow from the sump → Dug well

If dug wells are absent, construct recharge wells or percolation pits depending upon space
available
Consider a building with a flat
terrace area of 100 sq.m.
Average annual rainfall in Chennai
is approximately 1300mm
Assume that 60% of the total rainfall is
effectively harvested
Volume of. water harvested = 1,30,000 x
0.6 = 78,000 litres
213 litres of water/day will be available for
the household
This is enough to meet the drinking and
cooking needs of a household

4. Diversion of rainwater from the
terrace into a shallow dug well in
an apartment complex

5. Harvesting the Driveway Runoff

Rainwater that falls around the building is usually wasted

Not good for potable uses, but definitely worth using for recharge

Gutter near the gate does the trick

Water collected at the gate → Recharge well

6. Greywater Recycling
•Almost 60% of the refuse water from our daily usage is good, quality
sterile water - Can be easily cleaned up
•Plants remove all the organic material
•Water is further polished by soil bacteria as it travels down the soil
•The cleaned water can be safely used for flushing and gardening
•Excess can be put into the soil to augment the shallow water table
Daily Water Usage
Flushing - 35%
Kitchen - 15%
Bathing and Washing
of Clothes - 50%

7. Characteristics of a good groundwater recharge system
Both from Rainwater harvesting and Greywater recycling

Completeness -Both rooftop and driveway runoff water to be harvested.

Apportioning of water–To avoid overload of any one system, leading to overflow and loss.

Proper design - Volume of water likely to flow through and the nature of the soil in the area
should be considered.

Maintainability - Design should incorporate features allowing for periodic maintenance of the
structure.

8. Annual rainfall averaged over the last 50
years falling over the 174 Sq km area of
Chennai is 127cm.
If this is harvested, every citizen can get
135 litres per day
Chennai is rain-rich but water- starved

No perennial river nearby

Rain from SW and NE monsoons

Macro-supply - Reservoirs are woefully
inadequate
What should be done?

Reduce dependence on Metro water Supply

Increase dependence on sources within
one’s premises

Conjunctive use of aquifers – shallow &
deep
The Chennai Experience

9. Government Initiatives
Tamilnadu is the first state in India to make rainwater harvesting mandatory
1) Tamil Nadu Municipal Laws (Second Amendment)
Ordinance, 2003


Inserted Sec. 255A in the Chennai City Municipal
Corporation Act, 1919 which made Rain Water Harvesting
mandatory
Similar changes were made in Municipal laws of other
major cities as well
2) Rain Water Harvesting Structures in Buildings Amendments to Building Rules
3) Ground Water Potential Villages including Well field &
Suburban Area
4) Act to amend the Madras Metropolitan Area
Groundwater (Regulation) Act 1987
Rain Centre Chennai
RWH Survey - 2006
•After the record rainfall of 250 cm. in
2005, there was a phenomenal rise in
groundwater table
•Survey revealed that the Groundwater
table had risen by minimum of 6 m. and
a maximum of 8 m. in the entire city
•Shallow aquifer recharge very
successful -Temple tanks which were
previously empty had water in them