Designing a bathroom to be green requires ample forethought to plan from the plumbing up. Bathrooms in a typical house are the single largest consumer of water, consuming upwards of 60% of a homes annual water use. This can be reduced in a number of simple ways just by planning out your construction.
Toilets are the single largest consuming plumbing fixture in any home and can use upwards of 20 to 30 gallons a day per person. At 1.6 gallons per flush for newer toilets and 3 gallons per flush for older toilets that is a lot of wasted water. Simply purchasing a highly efficient toilet can resolve a lot of these issues. A dual flushing toilet is an ideal solution to this. Using 1.6 gallons for a standard flush and half that for liquid flushes. Homeowners can drastically reduce their consumption of water with just this one upgrade.
Showers are the next largest consuming item in any bathroom. The average shower head uses 5 gallons per minute but a newer high efficiency shower head can reduce water consumption to half that. That is up to 25 gallons per 10 minute shower.
If a bathroom is being planned from the ground up a more aggressive approach to green construction would have a gray water diverter valve which will store shower and sink water to irrigate outside and flush the toilet. This allows the water to be used twice.