Although most new toilets only use about a gallon of water per flush (and some use even less), older models are water hogs. Even if you have a newer toilet you may be wasting water without knowing it. With a little knowledge about how toilets work you can do your part to conserve water.
Displace some of the tank water
If you take off the top of your toilet tank, you'll typically see that all of the mechanical parts - the filler and flapper valves, overflow tube and float - are on one side while the other side is empty except for water. One simple trick is to place large plastic jug filled with water on the empty side which reduces the amount of water the tank takes on when it fills. Some people use bricks or other objects to displace the water, but be careful to choose something that will not break apart and put particles into the water -- which can get into the mechanism.
Replace the flapper valve
Even a newer toilet can waste water if its flapper valve is not closing tightly. The flapper is typically a thin rubber or plastic valve attached to a chain; when you flush your toilet, the chain pulls up on the valve, causing it to open and allow water to enter the bowl. To test if you have a leak, put food coloring into your toilet tank. If after 15 minutes the color shows up in the bowl, you have a leak.
Replacing a flapper valve is simple, and can be done by most homeowners. First, flush the toilet and measure how long the chain is when extended. Next, remove the chain from the flush lever, take off the old flapper by either sliding it up and off of the overflow tube, or unhooking its "ears" from the flush valve pins. Write down the make and model of your toilet, take that information and the valve to hardware store and get a replacement. Slide the new valve onto the overflow tube, seat it properly, and attach the chain. Test for leaks.
Adjust the water level
When your toilet refills its tank, there needs to be some mechanism that detects when the proper level has been reached. In older toilets this was done with a copper or plastic float ball attached to a metal rod. As the float ball rises, the rod shuts off the fill valve. To make your toilet more water efficient, you can bend the float rod downward slightly with your hands; this lowers the float ball and means the tank won't fill as much.
Change your filler valve
If you notice that your toilet is noisy when filling or takes a long time to fill, your filler valve may be to blame. This valve is often found on the left side of your toilet tank and is typically connected to a fill tube, your float, and the overflow tube. This valve allows water into the toilet after it has been flushed, and if it becomes dirty or damaged, it will not function as efficiently. As a result, water takes longer to get into your tank and extra water will be wasted going into the overflow tube.
In order to replace your filler valve, first shut off the water to your toilet, then drain the tank by flushing. You will need to unscrew the filler valve assembly from the water line on the outside of the toilet, and it will often be attached to the bottom of the toilet tank using a plastic screw cap. The entire assembly should come out in one piece, and you can start by trying to clean and replace the valve. If that does not work, take the valve assembly to a hardware store - they sell these assemblies as single kits. Many are adjustable, allowing you to change their height to match that of your toilet tank. Once you've replaced the valve, test your toilet. If it still doesn't fill properly, consider hiring a professional plumber to look at the problem and suggest a remedy.
Check your water line
Another simple way you can make a toilet more water efficient is by stopping any leaks. Often, these will occur where the copper water line meets your toilet, and they may show up as a pool of water on the floor or "sweat" on the copper line. Turn of the water, disconnect the line and take a look at the rubber gasket inside. After years of use, these rubber stoppers can deteriorate and will begin to let water seep through. If you feel pitting in the rubber or see rubber bits on the valve, pry out the gasket and replace it with a new one.
While older-model toilets can be the source of wasted water in a home, making them more efficient is possible with little effort and minimal cost.