My water bill crept up for three months before I noticed. Not by a lot each month, just a few dollars, the kind of increase you blame on the utility company and forget about. Then I heard the toilet. It was not the dramatic running sound you notice from the hallway. It was a soft, periodic hiss that I had tuned out months ago.

That quiet hiss was a leaky flapper valve, and it was sending water down the drain around the clock. A toilet with a slow leak can waste anywhere from a few dozen to a few hundred gallons a day. Mine was on the low end, and it still added up to real money.

Find the leak in one minute

Drop a few drops of food coloring into the toilet tank and do not flush. Wait fifteen minutes. If color shows up in the bowl, water is leaking from the tank into the bowl, and the flapper is your culprit. If the bowl stays clear, the leak is somewhere else.

The fix is a five dollar part

The flapper is the rubber valve at the bottom of the tank that lifts when you flush and seals again when the tank refills. Over time it warps, gets mineral buildup, or just wears out, and it stops sealing completely.

1. Turn off the water valve behind the toilet and flush to empty the tank.
2. Unhook the old flapper from the chain and the little pegs on the overflow tube.
3. Take it to the hardware store and match it, or buy a universal flapper kit for about five dollars.
4. Snap the new one on, reattach the chain with a little slack, and turn the water back on.
5. Flush a few times and check that the flapper seats fully and the hiss is gone.

That is the whole job. No plumber, no tools beyond your hands, no special skills. The first one took me twenty minutes because I was being careful. The next one will take five.

Watch the bill drop

The month after I replaced the flapper, my water bill dropped by about nine dollars. That is over a hundred dollars a year for a five dollar part and twenty minutes of work. If your leak is worse, the savings are even bigger.

One more check while you are in there: add a few drops of food coloring to the tank again after a week. If it stays clean, the fix held. If the color returns, the seat under the flapper may have mineral buildup, and a quick scrub with an old toothbrush fixes that.

I check both toilets in my house every few months now. The hiss is gone, the bill is down, and I no longer pay the utility company to pour water into a pipe.