back syphoning

[breezer]

I know the water board says you must have an air gap or anti syphon device for all "tanks" but has anyone ever known a tank to back syphon. I am not saying it can never happen, just curious

 

[bengasman]

It seems that water companies including Thames water are very concerned about contamination. Apparently bacteria are very keen to swim against the flow into the mains pressure. Pretty strong those little buggers are. If this causes dangerous contamination, I wonder what happens at the porous victourious
Rumour has it that Thames water have pledged to replace all the old pipe at a rate of many miles per year. Unfortunately they have so much pipe that the job is not likely to be finished anywhere this century, we only have 93 years left til the next one. I was told that for every gallon of water that comes out of our taps, half a gallon or more is lost by defective T.W. pipes. Don’t know if it is all true but it would not surprise me.

 

[ChrisR]

There's a famous, possibly apocryphal but who knows, story of a garden hose being left in a pond which had nasty chemicals in it. The mains was turned off and the pond water entered the main.

This isn't a tank/cistern, but if the float valve was letting by and the water level rose high enough and the overflow/warning pipe wasn't there or was blocked, then it could happen.

Takes about 3 faults though. The answer to your question is, for me,

"no"!

 

[breezer]

thanks guys, i thought so.

bengasman, they are repalcing the pipes in west london, they close roads and cause chaos when they do

 

[bengasman]

I know they do breeze, same here. the point is that according to some chap on talk radio who sounded like he knew what he was on about, at the current rate of replacement, miles of pipe devided by replaced miles per year, the job would take 120 years. i doubt if my customers would be satisfied if it took me that long to fix all the leaks in there house.