In the USA, that likely would require a backflow preventer of some type=20 by the EPA via your local water supplier. There are some rather stiff=20 fines for non-compliance I believe. There is then an annual inspection=20 required that costs ~$60. I have an 8000 gallon cistern (tank) and=20 collect all roof rain water. We use the water for washing, bathing. At=20 the kitchen sink there is a separate faucet for the city water for=20 potable purposes. The remainder of the house can be either roof or city=20 water with a switchover that is impossible to cross connect, and yet a=20 reduced pressure backflow preventer is required. On 4/7/2011 2:42 PM, M.L. wrote: > On Thu, Apr 7, 2011 at 1:05 PM, Denny Esterline wr= ote: > =20 >> Ok, looks like you've gotten more than a few good suggestions about >> flow meters, hard to argue with the $10 option. :-) >> >> But as far as gray water heat exchangers goes.... there's plenty of >> people before you: >> >> http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=3D= 13040 >> >> -Denny >> =20 > Had I thought I invented something new, I wouldn't have shared it with > all of you folks! > Certainly there's nothing new about a water-water heat exchanger. I > just want to put a figure on how much energy I'm reclaiming at > present. > My heat exchanger is a single-walled design, which although it is > perfectly safe, is probably not "legal." The potable water is of > significantly higher pressure than the gray-water, thus there can > never be any accidental contamination. It's also an order of magnitude > less expensive than the double-wall designs that use a 4" diameter > copper pipe for the drain water. > > There's more to the system, and I hope to put up a web page to show > some pretty graphs and things. > > =20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .