The basic idea behind water-saving devices is to restrict water consumption rates where heaviest use occurs. Indoor water usage runs about 40% for toilets, 30% for baths and showers, 15% for clothes washers and 15% for cooking and kitchen use.
The first target for water conservation is the toilet. Any new toilet consumes no more than 1.6 gallons per flush - but older models may consume as much as 7 gallons per flush. A dual flush mechanism and early closure flappers are two ways to save from 40 to 50% of normal water consumption. Leaks in the toilet tank can also be a source of excess water usage. Detect leaks by adding dark food coloring to the tank. After 20 minutes, check to see if the toilet bowl water has turned the same color.
Showers and baths are the next target for water savings. The most common way to regulate the flow of water is through flow control valves and flow restrictors. And low-flow showerheads will also help conserve water.
However, the biggest source of water waste is leaky faucets or pipes. Because of the wide variety of faucet washers available, it's usually best to visit your local Do it Best hardware or building center.