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My toilet bowl and tank water appear to have evaporated after several weeks of disuse. How should I go about getting water in them again? I haven't tried anything yet because I didn't want to do the wrong thing.

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    In future, if you are going to leave the toilets unused for a long time, a spot of cooking oil on the water surface will stop it evaporating as quickly.
    – RedSonja
    Commented Aug 1, 2022 at 8:29
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    You should start by turning back the water on for the whole house ? :-)
    – Jeffrey
    Commented Aug 1, 2022 at 17:11
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    Only several weeks? And you're sure there's no leak?
    – user19565
    Commented Aug 1, 2022 at 20:37
  • Note that the water in the bowl/trap and any other drain traps can go down quickly (even in hours) when it's windy. This is due to the Bernoulli effect of wind over the vent pipe, drawing water back into the sewer/drain. Commented Aug 4, 2022 at 4:23

4 Answers 4

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Given that evaporated toilet bowl (pan) water leads to sewer gas in the house, just dump a bucket or two of water in there as your first step. There's no wrong way to do that, nothing to damage by doing that, and a good deal of noxious awfulness that should be stopped as fast as possible. You can also fill the tank with a bucket so you can flush the toilet, until you sort out why it's not automatically filling.

Probably should run water into every trap in the house, if it's so dry the toilet water evaporated, other traps may also have evaporated.

If the tank (cistern) water has evaporated and not refilled automatically, either the water to the toilet is shut off, or the tank fill valve is stuck or defective.

So, fix either or both of those as applicable. Short-term could be as easy as jiggling the tank valve float to free it if it's stuck, or opening the shut-off valve if that's turned off. Long-term might be to replace the tank valve, if it keeps getting stuck.

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    Yes, most definitely put some water in there ASAP. It's a health hazard to have an empty toilet, as the trap may be empty too, which is very unsafe.
    – Mark
    Commented Aug 1, 2022 at 6:56
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    ... or the toilet is of a design where the bowl does not refill automatically, but only when flushing. This is the case for common toilet design e.g. in Central Europe. Commented Aug 1, 2022 at 19:16
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    @cbeleitesunhappywithSX not just Central Europe, it's the case with every toilet I've seen in the US. Commented Aug 2, 2022 at 0:20
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    The odd part indicating a stuck valve is the tank/cistern not refilling, and being empty, not the bowl/pan water evaporating. As already stated...
    – Ecnerwal
    Commented Aug 2, 2022 at 0:43
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    If you intend to leave the toilet unused for a long period, it maybe an idea to pour a small amount of oil into the bowl. This will reduce the rate of evaporation.
    – Aron
    Commented Aug 2, 2022 at 4:55
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Somewhat related: it's close to impossible that a whole, covered, tank of water (10 liters or so?) evaporated within a period measured in weeks. Even if you live in the desert and the toilet is in full sunlight for the entire day I'd be scratching my head.

So there is a leak somewhere. I'd suspect the "regular" outflow hole, if the toilet is more than a decade old one of the various closing rubbers have degraded or worn away. Ecnerwal's solution is a good one for the immediate problem but I'd have a look at this too.

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    Even for the European-style toilets with much smaller water volume in the siphon/bowl I've never seen that evaporated. Only drained due to leakage, and with these, empty siphon will basically mean a crack in the lower part of the siphon. Commented Aug 1, 2022 at 19:19
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    Or, for example, people familiar with seasonal cabins don't usually experience the toilet bowl evaporating dry while they are away, and that's typically months, not weeks.
    – user19565
    Commented Aug 1, 2022 at 20:39
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Borgh touched on this, but I think it's worth exploring a bit more in this case. It's odd that all the water from the bowl and tank are gone. In fact, the system really shouldn't let the tank ever go dry.

Your toilet consists of

  • A water line (with cutoff)
  • A fill valve (inside the tank)
  • A tank
  • A flapper attached to the handle
  • The toilet bowl itself

The way this works is that the tank fills with water via the fill valve. When you flush, you are mechanically moving the flapper up. It has a trapped pocket of air so it will float until the water in the tank becomes low enough for it to close again. Beneath the flapper is a drain that leads to the bowl. Most (but not all) of the water will go into the bowl directly, while some water will go down the sides of the bowl.

Now that the tank is mostly empty, the fill valve opens (it has a float attached to an arm). The fill valve should have a tube that goes over to the overflow tube of the flapper assembly. The fill valve tube allows the refill process to send water into the bowl (since the end of the flush process removes most of the water from the bowl by design).

It's quite possible your bowl could be empty. The bowl normally has water in it to prevent sewer gasses from coming up, and to help prime the flush process. If you plunge your toilet, you're moving water down the drain manually without moving the fill valve, so nothing replaces it. If left in this state, you could have your drain go dry. The bowl water is also more exposed, so it can evaporate more readily.

The tank, however, should never go dry. Even if you're leaking water from the tank, the fill valve should keep the water at its set level. Moreover, your lid should keep most of the water inside.

Assuming you've not turned your water line off, you'll need to check the following

  1. The flapper. The simplest (and cheapest) flappers are rubber. Unfortunately, they can also warp over time. If it's leaking you'll typically note water seeping into the bowl along the sides. It doesn't take much to let water seep out either. Check to make sure your flapper seats properly. A dry tank, most of the time, is caused by a bad flapper.
  2. If the flapper looks OK, make sure the whole flapper drain assembly is properly seated (you might need to remove the tank to check). The assembly typically has a rubber gasket at the bottom of the tank, and is held on by a compression ring under the tank (bolts hold the tank to the toilet). Rubber gaskets can degrade over time. Assemblies can also crack (especially if you have someone over-torque it)
  3. The fill valve. If the water is below the fill line of the toilet, the valve should be open and allowing water into the tank. If it's not, there might be a way to flush the valve (Fluidmasters have a way to do just that). If the valve doesn't work, just replace it.
  4. The tank itself. Run your hand between the tank and the toilet and on the bottom. Check for any moisture caused by leaks. I had a tank develop a crack and was letting water seep out

Fill valves and drain assemblies are relatively cheap. When in doubt, replacing them is seldom a bad idea. If you have a crack, there are water-proof epoxies you can use to seal the crack.

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  • Comments are not for extended discussion; this conversation has been moved to chat.
    – Niall C.
    Commented Aug 3, 2022 at 2:38
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Your tank isn't automatically refilling. This is due to -

  1. Inlet water to house has been cut off (?)

  2. Valve at inlet to house has been turned off (?)

  3. Valve to tank supply hose has been turned off (?)

  4. The float ball in the tank is stuck in the UP position. When fully up, it closes the fill valve. When the tank is flushed, the float goes down with the water level and the tank refills until the float reaches the full up position.

I think it is likely the latter. And, frankly, unless the temperatures were really high, it is hard to imagine that rate of evaporation - in a pet water bowl, sure. But indoors in a porcelain tank with the top properly placed and the float ball NOT stuck in the UP position, you may have a leak somewhere- tank to bowl? Bowl to floor? Internal works (fill valve and float assembly etc)? I'd check those. Good Luck

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