I think I have a leak - How do I investigate?

You can check for leaks by turning off all fixtures so no water is being used anywhere in the house. Then check the position of the water meter dial, wait for about 30 minutes, and then recheck the meter. If it hasn't moved you have a relatively water tight home. If it has, you may have a leak and you should start checking toilets, faucets, hose connections, etc. Toilets are the most common source of water leakage.