A running toilet can waste up to 200 gallons of water a day. I know because I checked my water bill after ignoring the sound for three weeks. It had doubled.

Fixing it took five minutes and cost nothing. I did not call a plumber. I did not even go to the hardware store.

Open the tank and look

Take the lid off the toilet tank. Set it somewhere it will not fall — a bath mat on the floor works. Look inside while the toilet is running. Nine times out of ten, the problem is obvious once you see it.

The toilet flushes when you push the handle. That lifts a chain attached to a rubber flapper at the bottom of the tank. Water rushes into the bowl. When the tank empties, the flapper drops back down and seals the opening. The tank refills. A float rises with the water and shuts off the fill valve when the tank is full.

If the toilet keeps running, one of those parts is not doing its job.

The three most likely culprits

1. The flapper chain is too short or tangled. If the chain is twisted or caught under the flapper, the flapper cannot seal. Unhook the chain and adjust its length so there is just a little slack when the flapper is closed. Too much slack and the chain can get caught. Too little and the flapper cannot close all the way.

2. The flapper is worn out. Rubber flappers degrade over time. If the rubber is cracked, stiff, or discolored, it will not seal properly. A new flapper costs about five dollars and clips on in thirty seconds. Take the old one to the store to match the size.

3. The float is set too high. If the float is positioned too high, water overflows into the overflow tube before the fill valve shuts off. Adjust the float down about half an inch — most floats screw up or down, or have a clip you squeeze to adjust.

The one-tool fix

You do not need a full toolkit. Your hands are the only tool you need for most toilet fixes. The flapper unclips by hand. The float adjusts by twisting or squeezing a clip. The chain unhooks with your fingers.

If you do need to tighten a bolt — like the one holding the handle lever — a pair of pliers or an adjustable wrench will do it. But most running toilet problems are hand-fixable.

Test your work

Flush the toilet and watch the full cycle. The flapper should drop cleanly and seal. The water should stop rising about half an inch below the top of the overflow tube. If the water stops and stays stopped, you fixed it.

Drop a few drops of food coloring into the tank. Wait fifteen minutes without flushing. If colored water appears in the bowl, the flapper is still leaking. Try cleaning the flapper seat — mineral buildup can prevent a good seal even with a new flapper.

My water bill went back to normal the next month. Two hundred gallons a day adds up fast.