Catching a leak before it becomes a floor

The soft spot always turns up somewhere you have walked a thousand times. Just inside the door, or the corner by the shower, or the floor of the wardrobe with the fresh tank behind the panel. You find it barefoot on an ordinary morning, press it with a thumb, and the floor gives about a quarter of an inch more than a floor is supposed to.

That quarter inch is usually about two years old. An RV floor is a laminated sandwich, and water that gets inside does not run back out of the bottom; it sits between the layers and takes them apart from the inside. By the time the surface gives under a thumb, the repair is structural. Fire and collision write off a small number of RVs. Water writes off a great many more, slowly and quietly, with almost nobody catching it while it happens.

Three different problems, all of them called a leak

Worth separating before you spend anything, because only one of the three is something a sensor on the floor can see.

Plumbing leaks. Pump fittings, the water heater connections, the toilet valve, a pipe that split over a cold snap. These put liquid water in a specific place at a specific moment, which is exactly the thing a leak sensor exists to notice.

Roof and seal leaks. Around a vent, the air conditioner gasket, a skylight, the seam at the front cap. Water gets in up there and runs down inside a wall, so it surfaces somewhere unrelated, or never surfaces at all until the damage does. A puck on the floor will not catch these, and nothing electronic reliably will. They are caught by getting on the roof twice a year and looking hard at the sealant, which is unglamorous, and is the actual answer.

Condensation. Not a leak at all, and constantly mistaken for one. Water on the inside of a wall in cold weather with no plumbing anywhere near it is usually you, breathing. That is a different post, and the fix is ventilation rather than sealant.

Three options, cheapest first

Look, and turn the pump off

Free, and better than most people manage. Open the wet bay when you arrive and again when you leave. Look behind the water heater. Run a hand along the floor at the back of the cabinet under the sink, because in there damp is much easier to feel than to see.

The other half of this also costs nothing: turn the water pump off when you leave the rig. A pump left switched on will happily push the entire fresh tank through a failed fitting and then keep running dry looking for more. Switch it off and the same failure becomes a puddle.

What none of it covers is the calendar: everything that happens while you are somewhere else, which for a stored rig is most of the year, plus every drip too slow to make a puddle worth noticing. A slow drip inside a closed cabinet is precisely how the expensive version begins.

The beeper from under the washing machine

The battery pucks sold for exactly that job: contacts on the underside, a piercing beeper, a few dollars each. Genuinely worth having, and if the rig lives on your driveway and you are in and out all week, this is an honest answer and I would not talk anybody out of it.

The design assumes somebody is in earshot, though, and a stored rig has nobody in earshot for months. Left in a compartment it beeps at nothing until the battery gives out, then goes quiet, and you meet it much later lying beside the damage it announced to an empty lot. That is the worst kind of failure, because afterwards it looks identical to a device that never had anything to report.

When the puck can reach your phone

Same puck, plus a radio. The SwitchBot Water Leak Detector is the one we support: drop it under the wet bay, behind the water heater, or beside the fresh tank, and it broadcasts leak state, tamper state and battery level. Anything speaking BTHome v2 with a leak field works as well, which takes in the Shelly BLU range and most DIY builds, and the compatibility database lists what we read from each.

Alert on the battery as well as on the leak. A leak sensor is a thing you fit once and then stop thinking about, which makes it the device most likely to have died quietly a year before the night you needed it. The battery reading is what tells you it is still on duty, and that is the reason to prefer a broadcasting puck over a beeping one even if you are always within earshot.

You pay for it, and there is a longer chain to keep working: the puck has to reach the hub, and the hub has to reach the internet, before any of it reaches you. In a storage lot with no connectivity you own a device that keeps a record rather than one that raises the alarm, which is the harder problem.

Low, and slightly off to the side

Water runs downhill and gathers at the lowest point it can find, so a sensor goes low and a little away from the fitting rather than directly beneath it. A drip will travel along the underside of a pipe for a surprising distance before it falls.

1. The wet bay floor. Pump, filter, low point drains, most connections. If you buy one sensor, it goes here.
2. Under the water heater. Tank fittings and the drain plug, and a slow weep here runs into the wall cavity rather than into the open.
3. Under the kitchen sink, at the back. Enclosed, out of sight, and where a supply fitting drips unseen for months.
4. Beside the fresh tank. Especially if it is inside the living space, where a failure is immediately a floor problem.

The bathroom floor matters less than people expect. It is built to get wet and it usually drains or dries. The cabinet behind it is where the trouble is.

Where to get one

One under the water heater and one beside the pump covers most of where plumbing actually fails.

The freeze that leaks a week later

A line that splits in a freeze does not leak while it is frozen, because there is nothing liquid in there to leak. It leaks on the thaw, often a day or two later, and usually while nobody is there for the first of it.

That makes a leak sensor a good companion to a temperature sensor on a stored rig, and a poor substitute for one. The temperature reading warns you before the damage. The leak sensor tells you it has already happened, hours before anyone would otherwise have noticed, which on a laminated floor is still worth a great deal.

So both, if you are storing somewhere with a real winter, and winterise properly regardless, because no sensor ever built has stopped water expanding. All any of them do is shorten the distance between something going wrong and somebody finding out about it. On that floor sandwich, the distance is the repair bill.