9.1 The RWH system
The harvesting of rainwater simply involves the collection of water from surfaces on which rain falls, and subsequently storing this water for use. The rainwater collected can be stored for direct use or can be recharged into the underground aquifers. In scientific terms water harvesting (broadly) refers to collection and storage of rainwater from the rooftops. This also restricts evaporation and seepage into building foundations. All buildings having a plot size of 100 sq.m. or more, while submitting the building plans for sanction, shall mandatorily include the complete proposal of rainwater harvesting.
A rainwater harvesting system consists of:
i. Roof catchment
iii. Down pipes
iv. Rain water/ Storm water drains
v. Filter Chamber
vi. Storage Tanks/ Pits/ Sumps.
vii. Ground Water recharge structures like pit, trench, tube well or combination of above structure.
Rainwater Harvesting is a way to capture the rain runoff, store that water above ground or charge the underground aquifers and use it later. This happens naturally in open rural areas. But in congested, over-paved metropolitan cities, there is a need to devise methods to capture the rain water. The rainwater that is incident on the surface/ roof top is guided to bore wells or pits or new/old/ abandoned wells through small diameter pipes to recharge the underground water which can be used later whenever required.
Rainwater can be harvested to the extent of 55,000 liters per 100sq. meters area per year from rooftops.
9.2 Rainwater harvesting techniques:
There are two main techniques of rain water harvestings.
a. Storage of rainwater on surface for future use.
b. Recharge to ground water.
The technical aspects and options of Rainwater harvesting from which the city authorities can assess and choose to adopt are placed at Annexure III to the bye-laws.
9.3 Harvesting provisions in various Building categories:
All buildings in a city contribute to the rainwater runoff during the monsoon and hence such runoff can be harvested for water reuse/recharge.
The indicative provisions of rainwater harvesting in various buildings types are:
Note: The number of recharge bores to be provided in different plot sizes shall be accordance to Sl No 2 of Table Nos. 14.1 - 14.3 of Chapter 14.(Climate Resilient Construction)
9.4 Rain Water Harvesting Provisions for Open spaces in cities
The open spaces/recreational land use generally constitute regional parks, district parks, play ground and stadium, sports complex, monument zones, public parking, Plaza and other public open space. This may be as high as 30% to 50% of the city’s geographic area. All such public open spaces above the size of 500 sq.m. shall have arrangements for complete utilization and capture of storm water with scientific rain water harvesting arrangements.
Following ideas may also be included:
i. Well cum Channel cum Percolation pits.
ii. Use of abandoned bore wells for recharging of ground water
iii. Artificial or natural Storage of storm water runoff from larger sites.
9.5 Ground Water Recharge
Recharging of ground water should be made mandatory not only for residential buildings but for all types of buildings, including Group Housing Societies having a plot area more than 500 sq.m. and above.
The Ground Water Recharge should also be mandatory for open spaces like parks, parking, plazas and playgrounds. The harvesting and recharge structures could be constructed by the Authority with the involvement of community based organizations like Resident Welfare Associations.
9.6 Enforcement and Monitoring
a. The Authority shall constitute a Rainwater Harvesting Cell which will be responsible for enforcement and monitoring of the provisions of Rainwater Harvesting. The cell shall employ qualified persons who are well versed with the interpretation of Building Bye Laws and responsible for enforcement as well as monitoring the functioning of the Rainwater Harvesting System.
b. The Authority shall include inspection of Rainwater Harvesting Structures before issuing Completion Certificates or NOCs for service connections to the property.
c. Set an example in the city by ensuring that Rainwater is harvested in the properties /assets owned by them including public buildings, markets, community centers, parking spaces, roads and parks etc.
d. The Authority shall also establish a mechanism to monitor 100% of RWH provisions in all the buildings above 1000 sq.m. with annual physical verification, while buildings less than 1000 sq.m. can be monitored on the basis of 10% random survey by competent authority.
e. With regard to open public spaces viz., Parks, playgrounds etc. the implementation of provision rainwater harvesting may be done with the help of Residents Welfare Associations, Community Building Organization and NonGovernmental Organizations.
f. The Authority shall ensure earmarking budgetary provision for the creation and maintenance of rainwater harvesting structures in public spaces owned and maintained by them, like parking spaces, parks, plazas etc
g. The practice of incentives and penalties to promote rain water harvesting shall be formulated by the local authority based on best practices. Authority shall design its own incentive and penalty systems, considering the water level and scarcity.