Every building in Chennai, old or new, is required to have a working rainwater harvesting (RWH) structure. The requirement was extended to existing buildings by a 2003 amendment to the state’s municipal laws, the ordinance text of which Chennai Metro Water publishes on its website. New buildings also need an RWH design in the plans submitted for approval.
The northeast monsoon set in over Tamil Nadu on 15 October, and IMD expects normal rain over south peninsular India this season. With Tamil Nadu getting close to half its annual rainfall between October and December, the next few weeks are when your RWH pit earns its keep. A pit that was dug twenty years ago and never cleaned is probably doing little. Here is how to check and fix it.
Why it still matters
The 2003 mandate is widely credited with a rise in groundwater levels across the city in the years after it was enforced. Groundwater has long supplemented the city’s rain-fed lakes, supplying up to 120 million litres a day at times, according to the World Bank, so every recharged pit counts.
The supply picture this year makes that clear. Chembarambakkam reservoir was at about 35% of capacity on 14 October, and the state has asked Andhra Pradesh for extra Krishna water. A ₹3,108 crore Ring Main System linking major drinking water sources is planned for completion by 2030-31, Deccan Chronicle reported from the state budget. Until then, borewells in many neighbourhoods depend on what the monsoon puts back into the ground.
The common types of structure
- Recharge pit or percolation pit: a pit filled with layers of pebbles, gravel and coarse sand that lets rooftop or yard water soak in. Common in independent houses.
- Recharge well or ring well: a deeper shaft lined with perforated concrete rings, used where the soil is clayey or space is short.
- Borewell recharge: rooftop water filtered and led into an existing or disused borewell.
- Storage sump: rooftop water filtered and stored for use. In apartments this is often combined with a recharge structure for the overflow.
A pre-monsoon check you can do in an hour
- Clean the terrace. Sweep leaves, dust, bird droppings and plastic off the roof. Whatever is on the terrace ends up in the pit.
- Clear gutters and down pipes. Flush each pipe with a bucket of water and check that the water comes out at the bottom freely. Fix cracked joints.
- Open the filter chamber. If the top layer of sand is caked with silt, scrape it off and replace it. If water pools on top for long after a shower, the filter media needs washing or replacing.
- Desilt the pit. Remove the top layer of silt and debris from recharge pits and wells. A pit that holds standing water a day after rain is clogged.
- Check the lid. Pits must have a secure cover so that children and animals cannot fall in and mosquitoes cannot breed.
- Look at the overflow. Overflow should go to the storm drain, never to the sewer line. Sewage must never be connected to an RWH structure.
- Test it. Pour a few buckets of water on the terrace and follow it all the way into the pit.
For apartments, the association should get the structures checked every year and record when it was done. Large complexes often have several pits; make sure each one has a working inlet.
Mosquitoes and safety
Dengue control drives are under way in the city. A blocked RWH chamber holding stagnant water is an ideal breeding spot, so keep lids closed and filters clean. If a pit sits beside a compound wall or foundation, make sure it is far enough away that water does not seep into the building. Ask a qualified engineer if you are unsure.
Where to get help
Chennai Metrowater publishes its own maintenance tips for RWH structures, which are worth reading alongside the checklist above. For technical advice, inspection or questions about compliance for a new connection, contact your Metrowater area office through the CMWSSB website. For new buildings, your architect should include the RWH design in the plan submitted for approval.
Quick answers
Is rainwater harvesting compulsory in Chennai?
Yes. It has been mandatory for all buildings, including existing ones, since the 2003 amendment to the state’s municipal laws.
How often should I clean my RWH pit?
At least once a year before the northeast monsoon, and after any heavy spell that leaves silt in the chamber.
Can I connect bathroom water to the pit?
No. Only rooftop and clean surface runoff should go in. Wastewater and sewage must go to the sewer.
Who do I ask for help?
Your Chennai Metrowater area office, listed on the CMWSSB website.
Information checked against official sources on 18 October 2026. Fees, dates and rules can change; confirm on the linked official pages before acting.
Sources
- Rethinking wastewater: Chennai’s journey towards water security (World Bank Blogs)
- Cooum, Adyar restoration back on agenda: TN budget 2026-27 (Deccan Chronicle, 6 Aug 2026)
- Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB)
- Tamil Nadu Municipal Laws Ordinance, 2003 on rainwater harvesting (CMWSSB, PDF)
- Maintenance tips for rainwater harvesting structures (CMWSSB)
