The Borewell Goes Deeper
The first thing you learn about groundwater in a city like this is that nobody can see it. Nobody knows precisely how much is down there, how fast it is being drawn, or how long the layer a particular building is sitting on will last. What people do know is the depth of their own borewell, because they paid for it, and the number only ever moves in one direction.
A borewell is a completely rational decision for a household or a housing society. The piped supply is intermittent. Tankers are expensive and of uncertain provenance. Drilling is a one-time cost that converts an ongoing problem into an asset on your own land. Everyone who can, does.
The difficulty is that an aquifer is not a set of private wells. It is a shared body of water that does not respect property lines. When the society next door drills deeper and pumps harder, the water under you drops too. The rational response is to drill deeper yourself. This is a textbook commons problem, playing out at a few hundred feet below a city of many millions, with essentially no meter on it.
Depth is the tell. Borewells that once produced at a few hundred feet now routinely go past a thousand in parts of this city, and the water that comes up from that far down is older, harder, and in some places carries dissolved minerals at concentrations that are a health problem rather than a taste problem. You are no longer drawing on this year's rain. You are drawing on a reserve that took a very long time to accumulate and will not refill on anything like the timescale you are emptying it.
What makes this specifically a city problem is what we have done to the surface. Rain that falls on soil soaks in. Rain that falls on concrete, tarmac and tile does not — it runs, fast, into a storm drain, and leaves. We have simultaneously increased extraction and removed almost every surface through which the aquifer could be refilled, then expressed surprise at both the shortage and the flooding, which are the same fact seen from two ends.
The fixes are known and unevenly applied. Rainwater harvesting works, and works better when the water is directed into a recharge pit rather than only into a storage tank. Treated wastewater can cover what does not need to be drinking quality, which is most of what a building uses. Permeable surfaces in parking areas and setbacks let a surprising fraction of the rain get back in. Lakes that are desilted and kept connected recharge the ground around them, which is one of the strongest arguments for restoration that has nothing to do with birds.
What is missing is not knowledge. It is metering and enforcement, and the reason those are missing is that they make an invisible free resource into a visible, costed one, which nobody enjoys being the first to propose.
I think about this every time I water the balcony, which is a trivial amount and not the point. The point is the habit of asking where the water came from, because for most of this city that question has an honest answer of 'somewhere under here, from before any of us arrived.' A city that never asks will find out anyway. It will just find out later, and all at once.