Family of five using about 5500 gallons a month. We are charged $70 by 2 different "Metro Districts" for water service and sewage processing before we pay a dime for actual water use. The actual water costs about $28 a month($.005G). Still, I feel compelled to save water whenever possible, especially if it's painless to do so.
Quick and cheap ways to reduce water use:
shower or bathe less if possible(my kids get two baths or showers a week)
place 2 or 3 beer bottles in your toilet tank(I put 3 in each of our three toilets cutting the flush from 3.5 gallons to just over 3, makes a huge difference with our family size)
install .5 GPM aerators on faucets(mine were 2.2gpm faucets so the aerators paid for themselves very quickly)
Additionally, we have a top-loading, water-saver washer and also just replaced our 1992 water hog dishwasher(12GPW) with a new efficient model(3.5GPW).
There is some truth to soaps acting like a fertilizer on a garden but the safety is certainly suspect. My in-laws used to live in an old cabin with inadequate septic for their family of 5. So at shower time, they plugged up the drain and caught all the water. Then my FIL used a bilge pump to send the water out the window to his gardens. He had the most prolific garden I've ever seen in my life. I *think* he just used the reclaimed water or his flower gardens but I'm not positive. Either way, the potential of dumping chemicals on the ground and into anything any living creature may consume is too great a concern for me.
There are graywater safe detergents available if anyone is interested:
http://5kidsonanacre.blogspot.com/2013/04/laundry-soap-grey-water.html