High water bills, especially those that are 5 to 10 times higher than average can indicate a leak in you plumbing system. On the lower end of the scale, this could be in the form of a running toilet or a leaking tap. If the bill is very high and there are no obvious signs of a leak in the house the most common issue will be a leaking or burst water main. These can be easily missed if the water main runs under a concrete driveway or though part of the property that is not often used. If you have a high water bill, you should immediately call a plumber and notify the service provider (watercare). In some cases the service provider should revert your bill to your normal average if you can prove you are working on fixing the issue as soon as possible.