Most Indian homes and buildings use the same basic setup: municipal or borewell water fills a ground-level sump (underground tank), and a pump lifts that water to an overhead tank (OHT) on the roof, which then feeds the taps by gravity. Automating this reliably is a genuinely two-sided problem — the pump can run dry if the sump empties below it, and can overflow if the overhead tank fills past full. A good automation system has to watch both ends at once. Here’s how it actually works.
Why one sensor isn’t enough
A lot of basic controllers only sense the overhead tank — they start the pump when the OHT is low and stop it when it’s full. That handles overflow, but it’s blind to the sump. If the sump runs empty while the OHT is still calling for water, the pump keeps running dry and damages itself. To automate a sump + OHT system properly, you need awareness of both tanks:
- Overhead tank level decides when the pump should run (OHT low = fill it) and when to stop (OHT full = overflow prevention).
- Sump level decides when the pump is allowed to run (sump has water = safe; sump empty = block the pump to prevent dry run).
The correct logic is the intersection of the two: run the pump only when the overhead tank needs water AND the sump has water to give. That single rule eliminates both the overflow and the dry-run failure modes.
The components involved
- A level sensor on the overhead tank — ideally non-contact (ultrasonic), mounted on top, reading level continuously.
- A level sensor on the sump — so the system knows whether it’s safe to draw.
- A pump controller wired in-line with the existing motor, executing the “run only when OHT needs it and sump can supply it” logic.
- Dry-run protection as a backstop — even with sump sensing, monitoring the motor’s own behaviour catches edge cases like a blocked suction line where the sump reads full but water still isn’t reaching the pump.
Handling the real-world complications
Municipal supply timing. The sump often fills only during municipal supply hours. A smart system learns that schedule — it knows the sump will refill at, say, 6am, so it can manage the overhead tank around that window rather than panicking when the sump is temporarily low.
Borewell as the sump source. If the sump is fed by a borewell that itself can run dry, you now have three water bodies to reason about. Fill-rate monitoring on the sump reveals when the borewell yield is dropping — useful early warning well before the sump actually fails.
Multiple overhead tanks. Larger buildings have several OHTs, sometimes for different pressure zones. Each needs its own level awareness, but they can share one sump and be sequenced so the pump fills them in a sensible order rather than fighting each other.
What good automation feels like day to day
Done right, you stop thinking about it. The pump runs when the overhead tank needs water and the sump can supply it, stops before either overflows or runs dry, and alerts you only when something genuinely needs attention — municipal supply didn’t arrive, borewell yield is dropping, or the pump’s behaviour has changed. No manual switching, no 2am overflow, no burnt-out motor from a dry sump nobody noticed.
Frequently asked questions
Can I automate just the overhead tank and ignore the sump?
You can, and it prevents overflow, but it leaves the dry-run risk open — if the sump empties while the pump is running, the motor runs dry. For a borewell-fed or municipally-fed sump that regularly runs low, sensing both tanks is what makes it safe.
Does this work if my sump and overhead tank are far apart?
Yes. The sensors communicate wirelessly to the controller, so distance between the sump, the pump, and the rooftop tank isn’t a problem — a system with good wireless range covers a typical building without extra cabling.
What if the same pump fills two different tanks?
That’s a common setup and it’s handled by sequencing — the system fills one tank, then the other, based on each tank’s level, rather than trying to serve both at once. Each tank keeps its own sensor and target level.
