1. Check Your Utility Bill
A place to start is to examine your utility bill for January or February. It’s likely that a family of four has a serious leak problem if its winter water use exceeds 12,000 gallons (or 16CCF) per month. You can also look for spikes - is your water use a lot higher this month than it was last month? Learn more about your water bill: http://1.usa.gov/1Qw3Eg9.
2. Read Your Water Meter
Find your water meter, which is usually near the curb in front of your home but can be inside your home (e.g., in the basement) in cold climates. Use a screwdriver to remove the lid on your meter, which is heavy and usually marked “water.” Now that you’ve found the meter, take a reading during a period when no water is being used. If the meter does not read exactly the same after two hours, you probably have a leak. Here’s a tip on how to read a water meter: http://bit.ly/1TeYnMu.
3. Take a Toilet Test
Put a few drops of food coloring into the tank at the back of your toilet and let it sit for 10 minutes. If color shows up in the bowl, you have a leak. Make sure to flush afterward to avoid staining, and consider replacing your old toilet flapper if it is torn or worn.