My water bill suddenly doubled. How do I find a hidden leak?

Concerns & risks

You opened the water bill expecting the usual and nearly dropped your coffee: it doubled. Nothing in your routine changed, no new hot tub, no extra guests. Somewhere water is escaping, and you can't see it.

A hidden leak can keep costing you money and slowly damage floors or walls.

Causes & evidence

Most surprise bills come from silent leaks: toilets, dripping faucets, outdoor spigots or irrigation. Background and numbers: household water leaks.

What to do

1. Turn off every tap and appliance. Find your water meter and snap a photo of the reading.
2. Use zero water for 2 hours, then read it again. If it moved, you have a leak.
3. Do the food-coloring test in every toilet (toilets are the usual suspect).
4. Check outdoor hoses, sprinklers and under every sink with a flashlight.

Common mistakes: A common mistake is reading the meter while someone runs the dishwasher or ice maker, which gives a false alarm. Make sure everything is off first. Don't forget outdoor spigots and irrigation lines; they're easy to miss. And don't ignore a small steady leak. Even a slow drip adds up over a billing cycle. If the meter moves with everything off and you can't find the source, a plumber can test lines you can't reach.

Speed Man tip: Meter moving but toilets and faucets are fine? The leak may be in a pipe underground or inside a wall. Call a licensed plumber and ask your water utility about a leak adjustment.

Wrap-up: Use the water meter: no water use for 2 hours, the reading should not move. Toilets are the most common silent leak, so test them first. If you can't find it, a plumber can trace hidden pipe leaks.

Want the why behind it? Read How a Toilet Tank Works (Fill Valve and Flapper) in the wiki.