The concern is the possibility of liquid, including any water that might=20 not meet potable (drinking) water standards into the city water main=20 (system). Although your other water pressure is low, if there is a water=20 main break at a lower level than your equipment, a vacuum could happen,=20 drawing the other liquid into the system. This can also happen for a=20 variety of other causes including a pump or it's power failure. http://en.wikipedia.org/wiki/Backflow_prevention_device http://www.watts.com/backflowprevention On 4/7/2011 4:33 PM, M.L. wrote: > On Thu, Apr 7, 2011 at 3:50 PM, Carl Denk wrote: > =20 >> In the USA, that likely would require a backflow preventer of some type >> by the EPA via your local water supplier. There are some rather stiff >> fines for non-compliance I believe. There is then an annual inspection >> required that costs ~$60. I have an 8000 gallon cistern (tank) and >> collect all roof rain water. We use the water for washing, bathing. At >> the kitchen sink there is a separate faucet for the city water for >> potable purposes. The remainder of the house can be either roof or city >> water with a switchover that is impossible to cross connect, and yet a >> reduced pressure backflow preventer is required. >> >> =20 > > I'm not actually using the water for anything other than it's waste > heat. It only goes down the drain. > =20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .