There is a company called Water Saving Technologies who devloped an easy system to save water and money.

The Aqus System basically recycles and clenese the water from your bathroom sink and uses it to flush the toilet. 

The system is expected to save 8 gallons a day based on a 2 person bathroom. That's 2920 gallons a year. A quick check with your utility bill will give you an idea of the yearly saving.

The system was featured Best Of What's New 2007 in Popular Science magazine in the article "Guilt Free Flushing".

The draw back is the approximate cost of $295.00 but this will be recouped by the savings over time.

For a business or frequently used bathroom for a larger family this could some equate to savings.