Keeping historic readings of your meters is extremely useful. I made a habit of scanning in the bills I got from my water company, which showed that on average

Keeping historic readings of your meters is extremely useful. I made a habit of scanning in the bills I got from my water company, which showed that on average I was using ~40m^3 of water a year - I'm very conservative with water. In 2015, a bi-annual bill dropped through my door asking for payment for 120m^3 of water in six months. I hadn't changed my usage patterns, and by phoning them and quoting the previous bills, they quickly agreed it was extremely unlikely I was using four times my annual supply in half the time. They took it from there, investigated and discovered a leak just after my water meter (under panels in the road). From my previous bills, they quickly agreed to knock 99m^3 off my bill, bringing it in line with my usage.