Stubborn ancient bib tap

[JohnW2]

It is, but the point I was trying to make was, the check valve can fail, and therefore, if left say in a pond, the pond water can be back flowed into the supply.

True, but only if there is, simultaneously, a major (and rare) problem of supply pressure.

In any event, I thought you were trying to 'justify' the requirement for a check valve. If so, pointing out that they can fail is hardly furthering that argument - unless you are suggesting that the requirement should be for two or more check valves in series

Anyway, this whole tangential discussion was just an 'afterthought', and I do not disagree that 'a regulation is a regulation', whatever one personally feels about it.

Kind Regards, John

 

[JohnW2]

I know that's your view, it really isn't mine. Do you know how often backflow incidents happen?

No - do you?

Kind Regards, John

 

[RandomGrinch]

if contaminated water somehow gets into the end of a hose pipe (which itself must be pretty rare) it would require an incredibly iumprobable combination of ('rare') circumstances for that water to be able to 'backflow' through the entire length of the hose into 'other water' within the installation,

Outside taps connected to a hose, are often left turned on; the spray gun being used to control the flow.
A hose full of water, left out in the sun, would be a suitable breeding ground for bacteria.
The single check valve in outside taps are known to fail due to frost damage.
Local contamination to the drinking water within the house can be possible.

It has surprised me before, the number of threads on here, mentioning blue tap water - eventually being tracked down to contamination and backflow from a toilet cistern with blue cistern blocks.
...given that this can even happen - perhaps we should make blue cistern blocks compulsory, just to make the problem discoverable!

 

[denso13]

No - do you?

No. It really wasn't a trick question, but you've decided it's a rare event and people are being ultra cautious. But you don't actually know how often it happens

 

[JohnW2]

Outside taps connected to a hose, are often left turned on; the spray gun being used to control the flow. A hose full of water, left out in the sun, would be a suitable breeding ground for bacteria.

Fair enough.

The single check valve in outside taps are known to fail due to frost damage.

I was not actually thinking of 'single check valves' but, rather, of things like this (although I'm a little surprised that they can get everything into the small amount of space available:

It has surprised me before, the number of threads on here, mentioning blue tap water - eventually being tracked down to contamination and backflow from a toilet cistern with blue cistern blocks. ...given that this can even happen - perhaps we should make blue cistern blocks compulsory, just to make the problem discoverable!

I suspect that most commonly (maybe nearly always) happens in the context of an 'upstairs' toilet cistern, which rather moves the goalposts, since there is then an appreciable hydrostatic pressure to drive backflow. On the other hand, garden hoses (which is what we're talking about) are generally used close to ground level, hence not appreciably above the level of any of the pipework within the installation.

I suppose that there might therefore be an argument that there should be a requirement for check valves in all water feeds to 'upstairs', rather than to garden taps

Kind Regards, John

 

[denso13]

I suppose that there might therefore be an argument that there should be a requirement for check valves in all water feeds to 'upstairs', rather than to garden taps

Depends on the air break and fluid category as per the regs. Basin and bath taps tend to have an air break and therefore can't be submerged. However, a bath/shower mixer tap could have a hose which can be submerged therefore a check valve(s) may be required.

 

[JohnW2]

No. It really wasn't a trick question, but you've decided it's a rare event and people are being ultra cautious. But you don't actually know how often it happens

I think you are somewhat over-interpreting what I've written. I have never claimed to be stating facts, merely indicating what I (rightly or wrongly) think/feel, admitting that I may be wrong and, indeed, initially following that by asking 'what I was missing?'.

...as I said, I would have thought it was 'incredibly improbable'.

Maybe you're right, but I find it very hard to understand/believe.

Maybe I'm wrong, but it seems to me that .....

I would think it extremely unlikely that ....

I don't think that any of that is materially different from you expressing your view/opinion, which differs from mine.

Some of my 'feelings' are based on empirical observation. Backflow from something close to ground level (e.g. a hose) can only happen if the water pressure within the installation is very low (or negative) and, in all the many decades I've been using water supplies, I'm not sure that I have ever known the available water supply to 'reduce to a trickle' other than as a result of breakage in an underground supply pipe (in which case, as I've said, the supply will already have been contaminated).

As I've just written, backflow from 'upstairs' parts of the installation is far more likely but, ironically, as far as I am aware there is no requirement for check valves in pipework supply water to upper floors of dwellings!

Kind Regards, John

 

[denso13]

as far as I am aware there is no requirement for check valves in pipework supply water to upper floors of dwellings!

I've just explained there are sound reasons for that, which you probably haven't seen yet.

 

[JohnW2]

Depends on the air break and fluid category as per the regs. Basin and bath taps tend to have an air break and therefore can't be submerged. However, a bath/shower mixer tap could have a hose which can be submerged therefore a check valve(s) may be required.

Yes, but he was not talking about any of those things but, rather, toilet cisterns. In that case, whether or not the design is such that there is meant to be an air break, he has indicated that backflow sometimes is reported - but I am not aware of any requirement for check valves in such a situation.

In any event, what RandomGrinch has said suggests that air breaks may not be a panacea. If 'stagnant' water in a hose can breed bacteria, to subsequently be 'sucked' into the installation's pipework, then the same can presumably happen in run of pipe to an upper floor in which there has not been any flow for a long time.

Kind Regards, John

 

[JohnW2]

I've just explained there are sound reasons for that, which you probably haven't seen yet.

See my post which follows yours

 

[denso13]

Yes, but he was not talking about any of those things but, rather, toilet cisterns.

I quoted you, not him. You brought up supply water to upper floors.

as far as I am aware there is no requirement for check valves in pipework supply water to upper floors of dwellings!

Apologies if you only meant wc cisterns.

 

[JohnW2]

I quoted you, not him. You brought up supply water to upper floors.

I did.

Apologies if you only meant wc cisterns.

I didn't really mean just that, so you don't need to apologise

As I subsequently wrote, using his theory about 'stagnating' water in hoses (hence presumably also pipes), there would presumably theoretically be a risk in relation to any pipe which ascended to a significant distance above ground-floor plumbing level, regardless of air breaks or fluid category.

Kind Regards, John

 

[denso13]

As I subsequently wrote, using his theory about 'stagnating' water in hoses (hence presumably also pipes), there would presumably theoretically be a risk in relation to any pipe which ascended to a significant distance above ground-floor plumbing level, regardless of air breaks or fluid category.

Then, if your risk assessment of the plumbing design thought it was a problem likely enough to occur you should put measures in place to stop it happening. I'd suggest stopping legionella forming in domestic pipework would be the priority, not stopping the resultant legionella backflow.

Check valves are simple to fit (usually) if required. On toolstation the hose tap with check valve is 10p more expensive than the one without. For two on clearance the one with the check valve is actually cheaper. You can get a double check valve for less than a fiver. I don't think it is unreasonable to do at all, if deemed required.

 

[denso13]

(hence presumably also pipes)

There are regs in place to prevent legionella in pipework (temps/dead legs etc). No such rules for hoses.

 

[JohnW2]

Then, if your risk assessment of the plumbing design thought it was a problem likely enough to occur you should put measures in place to stop it happening.

Sure, but we're talking about regulations - just as with electrical matters, what I would personally do in my house (on the basis of my own 'risk assessment') may often differ from what regulations 'require', hence what I would tell/advise others 'should be done'

I'd suggest stopping legionella forming in domestic pipework would be the priority, not stopping the resultant legionella backflow.

That sounds logical, but I'm not sure how one would set about trying to 'stop Legionella forming' in cold water pipework through which there was no flow.

Check valves are simple to fit (usually) if required. On toolstation the hose tap with check valve is 10p more expensive than the one without. For two on clearance the one with the check valve is actually cheaper.

I don't think anyone has suggested that cost, or non-simplicity of fitting, are an issue - although I would point out that I was told early in this thread that check valves incorporated into 'hose taps' were not generally 'acceptable'. However, standalone check valves are cheap enough, and easy enough to fit.

You can get a double check valve for less than a fiver. I don't think it is unreasonable to do at all, if deemed required.

As I've said, if it is 'required' (by regulations), then that's what people have to be advised to do. However, that doesn't prevent one having a personal view about whether or not the requirement is addressing a significant 'need', rather than being done 'because it can be done' or 'to address an extremely small risk'. We have seen this a lot in relation to electrical matters, currently probably most apparent in relation to SPDs and AFDs, which are gradually moving in the direction of becoming 'more required'!

Kind Regards, John