Average Water Usage

Showers are required by Federal American law to use less than 2.5 gallons per minute.
The average shower uses about 7-8 gallons per five minutes.

A normal toilet uses anywhere from  3.5-7 gallons per flush.

Standard sink faucets use 1.3-2 gallons per minute.

http://www.epa.gov/WaterSense/pubs/indoor.html
http://wiki.answers.com/Q/How_many_gallons_of_water_per_minute_does_the_average_shower_use
http://www.cornerstonesmud.com/id46.htm
http://sogweb.sog.unc.edu/Water/index.php/Household_Water_Efficiency:_Faucets