Do we need a backflow preventer ?

Old 12-21-17, 12:21 PM
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Location: Mexico
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Do we need a backflow preventer ?

We never had a setup like we have now when we lived in the US - but I suspect people have somewhat similar setups - particularly people who collect rain water.

We have a community well - which provides water at the street perhaps half the time (very random). Because of this randomness we have storage tanks. We have a 1100 L tank on the roof which can receive water directly from the street (if the water pressure is good enough) or we can pump water up there (from our in ground tanks). So that tank on the roof feeds water to the house using gravity - although we do have a setup to increase the water pressure so we can really get a strong shower.

We have a smallish in ground tank (maybe 5 meters square) which is used to principally feed the sprinkler system.

We just built a new in ground tank (perhaps 18 meters square) which we plan on using to pump water to the roof if it is needed.

We just added a little bit of chlorine to all three tanks (as there is nothing added to the well water at its source).
We have a cheapo filter at the street to keep out dirt. And we have the same cheapo filter at the tank at the roof. We have a 5 filter RO system under the kitchen sink. We only drink water from that sink.
We have a $10 gauge at the street to tell us if there is water pressure. We also have a $100 wireless water level gauge sitting in the tank on the roof which tells us if we need to pump water up. Yes, we could set the pump on automatic - but because of the way things are prioritized, we know that if the tank on the roof is full, the two in ground tanks are also filled.

Our lot tilts down slightly. The two in ground tanks are lower than the house. Without the use of the pump - I can't see any
chance water from those tanks ever going up hill. BUT (and this is the root of my question) I do not understand what is keeping the water on the roof from going back out to the street.

For all three of our tanks the water is 'potable' (although we would never drink it directly. Is a backflow preventer used solely to keep the contamination of the drinking source OR might we need a backflow preventer to assure the water stays on the roof (since we pay for the water by the cubic meter).

Sorry for rambling - Thanks for your opinion.

Edit : I guess I just answered my question in my head. The water going into the tank on the roof comes in at the top - goes out at the bottom. So the water source is above the water line of the tank.

Last edited by lhpdiver; 12-21-17 at 12:40 PM.
Old 12-22-17, 10:13 AM
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I think you got it for the above-ground tank.

You can also use backflow preventers on the pump lines to keep them primed, so the water doesn't drain out of the pipes when the pump goes off.

Does anyone there use UV filters to help with bacteria? Chlorine used in the right amounts will obviously work, but it would seem difficult to keep adding at the right amount in each tank. Or maybe your body just gets used to what's in the water?

Even though you drink only out of the RO filter, showering, washing hands, etc. I'd imagine could be a problem with bacterial questionable water.

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