I am completing the Certificate in Sustainable Growing through Otago Polytechnic and as part of my sustainable water use module we were given a link to a water use calculator. While I am sure that it is not entirely accurate to the last drop it does give you a very good indication of how you compare to the average.
My score was 287.05/person/day with the average for NZ 250L/person/day. Considering we do not have a dishwasher, very rarely wash our vehicles ;), don't have a spa or pool, only 1 toilet etc I'm not all that surprised we were about average. Must get my hunny to reduce his time in the shower!!!
In Australia they are trying to get people down to 155L/person/day! Now there's a goal to aim for.