UPSC Mains 2018 GS Paper 1 Q14: model answer

In 2003 Tamil Nadu made rooftop rainwater harvesting compulsory for all buildings, and Chennai's water table rose in the following years. By June 2019 the city's reservoirs had run dry and 'Day Zero' headlines went round the world. Both events hold the lessons for making harvesting work in cities.

The problem

• The Central Ground Water Board reports many urban blocks as over-exploited; Bengaluru, Delhi and Chennai pump far more than nature recharges.
• Concrete surfaces stop rain from soaking in; most of it runs off into drains.

Why harvesting suits cities

• Large roof and paved areas collect huge volumes; a 100 sq m roof in a city with 1,000 mm of rain can capture about 1 lakh litres a year.
• Cheap, decentralised and quick to install.
• Reduces urban flooding by holding back storm runoff.

Why it often fails

• Systems installed only on paper to get building approval.
• No maintenance: filters choke, pits silt up.
• Poor design for local soil and aquifers.
• Encroachment of lakes and wetlands that once stored water.

How to make it effective

• Mandate with monitoring: geo-tagged systems and annual inspection, with property tax rebates for working systems (as some cities like Indore offer).
• Design to local geology: recharge wells in hard-rock Bengaluru, recharge pits and trenches in alluvial Delhi.
• Public spaces: parks, roads, playgrounds and campuses with recharge structures; Delhi's Jal Board guidance.
• Revive lakes and stepwells: Hyderabad's Mission Kakatiya-style tank restoration, Bengaluru's lake rejuvenation.
• Sponge-city planning: permeable pavements, bioswales and green roofs.
• Community and RWA ownership, school campaigns, Jal Shakti Abhiyan: Catch the Rain (since 2021).
• Integrate with reuse: treated wastewater for non-drinking uses reduces pumping.

Is it the 'ideal' solution?

Harvesting is necessary but not sufficient. Cities must also cut leakage (often 30–40% of supply), price water sensibly and regulate borewells. Combined, these can stop the slide in urban groundwater.