If you have a heavy leak in your toilet, it's easy to diagnose — the faint sound of the toilet tank constantly replenishing is a dead give-away. What about a slow leak? Diagnose it with food colouring.
If you have a slow leak in your toilet tank, hundreds of litres are just slowly and silently cascading down the side of your toilet bowl every month. Fortunately you can easily detect if the uptick in your water bill is from a slow leak or not.
Over at wikiHow they share a simple test for toilet water leaks, place a half dozen or so drops of food colouring in the toilet tank. Leave the toilet alone for a half hour or more. Come back and check to see if the water in the bowl of the toilet has become tinted with the food-colouring dye from the tank. If it has, you've got a leak between the tank and the bowl.
Check out the full guide at wikiHow for more details and how to fix the leak if you find it. Have a cheap way to test for problems around the house? Let's hear about it in the comments.