I have a second floor toilet- only 4 years old- that has suddenly started losing water (in the bowl)- It refills after flushing then slowly over time loses the water- I have looked all round the floor and bowl and there is no sign of a crack or a leak- Is there soemthing I can do before replacing the toilet. It is one four toilets in our house (there is one on the first floor and 2 abouve it on the third floor- none of the others have this problem- thanks for you help

If there is no sign of a leak anywhere, I would suspect the venting of the plumbing stack. If the stack (the 3- or 4-inch pipe which rises through your house, to which all the toilets and other fixtures are connected) is not properly vented, when other nearby fixtures are used, they can create a siphon effect which will draw the water out of the toilet bowl. If this never happened before, but does now, perhaps a vent has become partially or completely clogged by an item such as a bird's nest.

Just a guess by a non-plumber. Real pros are welcome to tear apart my thinking if it needs it. But, toilets are simple things, with no moving parts outside of the tank, so it's possible that you might replace the toilet and still have the same problem. The water is either leaking out, in which case you would know it because something would be wet or stained, or else it's being siphoned out. I don't think it can be much else.

There is nothing at all wrong with Mr Hetzel's thinking. Sometimes the porcelain can crack internally though and allow the bowl water to seep away slowly down the drain. If it gets bad enough it can affect flushing as well. There has also been some talk on this board of wind hitting the vent and affecting the bowl water level as Richard describes.

If the problem started suddenly without any other changes having taken place, I would suspect the toilet itself first, but there really is no way to test that without changing it out.

Good luck!