The sensor decides whether a water level controller still works in five years. The controller box rarely fails; the part sitting in or over the water does. Here are the four common types and what each one is good at.
Float switch
A float rises with the water and flips a switch at one height.
- Reads: one level only — usually "full" or "empty".
- Touches water: yes.
- Fails by: sticking. Scale, moss and debris jam the float or its hinge. The cable to it also wears out on a terrace.
- Use it for: a simple cut-off where a single level is enough.
Steel probes
Stainless steel rods hang into the tank at different heights. Water conducts between them, so the controller knows which probes are under water.
- Reads: a few fixed levels — typically four.
- Touches water: yes.
- Fails by: scale building up on the probes over time, especially in hard borewell water.
- Use it for: a budget, wired setup close to the pump.
Ultrasonic
A sensor above the water sends a sound pulse and times the echo from the surface.
- Reads: a continuous level, in centimetres.
- Touches water: no.
- Fails by: condensation on the sensor face and foam or ripples on the surface, both common in a closed tank in summer. The reading jumps or drops out.
- Use it for: open tanks with a calm surface.
Radar
A radar sensor above the water sends a radio signal and measures the distance to the surface, much like ultrasonic but with radio instead of sound.
- Reads: a continuous level. The 24 GHz radar we use reads from 0.15 to 10 m, to within 3 mm.
- Touches water: no.
- Fails by: very little — it is not bothered by condensation, temperature or a dirty surface the way ultrasonic is. It costs more than a float.
- Use it for: overhead tanks and sumps where you want the exact level and no maintenance.
Side by side
| Float | Probes | Ultrasonic | Radar | |
|---|---|---|---|---|
| Continuous level | No | No | Yes | Yes |
| Touches water | Yes | Yes | No | No |
| Condensation / foam | Not affected | Not affected | Affected | Not affected |
| Maintenance | Clean the float | Clean the probes | Wipe the face | None |
What we use
Every Nexomatic water level controller kit uses a contactless 24 GHz radar sensor, from the AquaPilot View kit at ₹7,499 to AquaPilot Solar Pro at ₹14,699 (incl. GST). Nothing sits in the water, and the solar kits need no wiring at the tank.