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Addressing backflow risks in Wet/Bathroom design


TerryE

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This issue is one that you could come a cropper with your BInsp if you aren't careful.  Here is a good paper written for WRAS which explains the issue and figure 2 is the nub of this issue

Zone of Backflow Risk.jpg

 

You have to prevent the risk of backflow at two separate risk levels:

  • (FC3) For basins and baths you can use double check valves, a self cancelling diverter (one of those button ones where the button pops if the flow stops), or a guaranteed airgap
  • (FC5) For anything where liquids containing shit or its micro-orgamisms can pool, and in particular for toilets and bidets, these must  be air-gapped with no exceptions. 

An airgap means just that.  In old indirect systems that were fed from a ballcock, using the indirect hot and cold on the shower feeds would meet this requirement but on pressured systems there is no such airgap internal to the pipework.  What this means is that the hose nozzle must be physically prevented from being able to be dropped into an adjacent loo or bidet.  This means that you have to ensure that the hose is either too short for the nozzle to reach or that there is some restriction that effectively limits the hose length to achieve the same, such as a fixed shower screen between the pair or a permanent restraining clip around the hose.

 

If the geometry / layout of your room means that this is a risk then using a very short hose or a permanent restraining clip to prevent this is the minimum that you should anticipate needing to get sign-off.  How permanent this constraint is after the sign-off is up to you and your conscience, but this is a real risk to the water supply.

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I thought this was going to be the "swap contents" issue mentioned in another thread.

 

When we had our supply connected by Scottish Water, it was made clear we must have a double check valve at the source, so there is one in line to the feed to our static 'van one in line to the site outside tap, and there will be one in line as the water enters the house.

 

do I take it that double check valve at source, sorts out ALL the issues of e.g where the shower hose will reach?
 

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The probability of back flow occurring must be quite rare. I think you would need to leave the shower head in the basin/loo AND leave the shower taps on AND for there to be a problem with the mains pressure?

 

The usual solution is one of those annoying rings you find on the shower head rail in hotels. Google suggests it's called a "Category 5 compliant security hose retaining ring"..

 

https://www.amazon.co.uk/MX-Shower-Hose-Retaining-Ring/dp/B00B2KFHUA

 

https://www.amazon.co.uk/Trueshopping-Universal-Shower-Retainer-Chrome/dp/B00KRAQ18I/ref=pd_sbs_60_3?_encoding=UTF8&psc=1&refRID=XYMSKAENNVXSZBG0MRNR

 

 

 

 

 

Edited by Temp
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Ok, let's clear this up. 

Situation could be....

Little Timmy decides for whatever reason to put the shower head in the ensuite in the loo. He walks off and plays Minecraft, blissfully unaware that the shower wasn't fully turned off after its last use. 

Meanwhile.....a plumber turns up and greets mum downstairs. "I'm here to fit your new kitchen sink tap luv". He turns off the stopcock ( which has the non return valve above it ) and opens the kitchen sink taps to let the hot and cold drain down. He goes upstairs to open the taps in the master bathroom and heads back downstairs to fit the new tap ( unaware that there is an ensuite ).

After fitting the new tap, the plumber ( good looking welsh guy most probably ) turns all the taps back off and turns the mains on. He tests for leaks ( Da iawn, wrth gwrs ? ) and collects his payment and leaves. 

 

Sounds ok .........? No. 

 

With the water turned off and the kitchen taps open a vacuum was created. That allowed water to be sucked ( syphoned ) through the partially open shower valve, into the shower hose, out of the toilet, and then into the entire cold water system. It then has time to contaminate the pipework for the time the plumber took to fit the new valve. 

Timmy then has to brush his teeth upstairs before bed and the water that first comes out of the tap may have been part of yesterday's evening meal. 

Mum then fills the kettle and that's not great either. Even worse she fills the ice cube tray at the same time and the American fridge pulls it all in too, to be dispensed for the rest of the evening.  

 

@ProDave, that tells you how much protection your 3-4 NRV's would provide in this situation. ZERO ! ?

 

Admittedly, the above is absolute worst case scenario, but hopefully allows you all a slightly rough as toast scenario / example to help understand why that type of reg is in place ;)

 

B|

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If you read that brief that I linked to FC1-5 is about protecting the public supply, and not necessarily about protecting the household.

Quote

In England and Wales, the Water Supply (Water Fittings) Regulations 1999 (and equivalent byelaws and regulations in Scotland and Northern Ireland) specify that there must be adequate devices at outlets to prevent backflow. The risk from backflow at any particular outlet is assessed in terms of fluid categories – the least serous being fluid category one (FC1) which is drinking water as supplied by Water Suppliers, and the worst being fluid category five (FC5) - fluids containing faecal micro-organisms as would occur in WCs. Backflow must be prevented by use of a suitably-rated device. Lists of devices and the backflow protection they give are included in the Regulations.

 

The difference between FC3 and FC5 as I read it is that for FC5, mandates a suitable air gap; a double check value (or even 2 in series) isn't good enough.  In older non-pressurised systems this could be achieved by feeding the shower from indirect H/W and C/W primed from a cistern, with the cistern filled from a ball-valve -- and thus creating the airgap between the shower tap supply and the public supply.  (This would not protect other indirect-fed basins fed fro the same indirect supply in the scenario that Nick discussed, BTW.)  The problem is that this type of gap doesn't exist with modern pressured systems, so the Building Inspector should therefore fail any configuration which breeches this guideline.

 

The easiest way to avoid any issues during inspection would be to comply with it by fixing short hoses or adding "permanent" restraining rings on the hose lines so that any shower hose passes the "can't reach the pan" test.  Whether you remove it or not after the inspection is your affair.  You might feel that a decent double check valve in the shower feeds should be perfectly adequate, but if you do and this does fail then you would be legally liable for the contamination that occurs.     

 

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Imho the risk of that back contamination is near zero. 

The scenario as Ive given above, which basically describes how this back flow contamination risk is born, incorporates a consideration to the volume of water needed to actually form such vacuum / siphoning and displays how hard it actually would be to put anyone OTHER than the householder at risk.

If the shower handset went into the loo it would siphon about half a litre or a litre at the absolute most before the siphon ended and the backflow ceased. 

If, and I mean IF, the contaminated water got through the household pipework and into the network mains, and then got to the branch where the house was fed from then I'd go and buy a lottery ticket. 

With the NRV at the stopcock ( or in Dave's case multiples of NRV's ) stipulating that the shower handset shouldn't get into the loo because it could contaminate the network water is quite questionable. 

If the loo was constantly flushing and could maintain a siphon then MAYBE, but the odds of that 'perfect storm' scenario just don't seem to make this as big a risk as it's considered to be. 

Id rather consider the risk to the householder, which is imo the real one.

;)

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In our new build, there is no way the shower will reach the loo.  In fact in our present house there is no way the shower will reach the loo.  BUT as I understand it, the current regs say a shower hose will not  reach the bath water or even the shower tray, that's why they provide those silly loops that leave the hose so constricted you can't even clean the shower properly. Are they worried you will pee in the bath, then nick's scenario will happen and you will contaminate the whole street? 
 

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42 minutes ago, Nickfromwales said:

IMHO the risk of that back contamination is near zero...

Two comments:

  1. Repeating what some once said to me: "when have you ever been f**king humble in expressing your opinions?"; stick to IMO :) That's what I  do.
  2. IMO, this debate isn't about real risks, it's about passing the inspection.  
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23 minutes ago, TerryE said:

Two comments:

  1. Repeating what some once said to me: "when have you ever been f**king humble in expressing your opinions?"; stick to IMO :) That's what I  do.
  2. IMO, this debate isn't about real risks, it's about passing the inspection.

Quite agree. Another job for the "after completion certificate has been issued" list.
 

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12 hours ago, TerryE said:

Two comments:

  1. Repeating what some once said to me: "when have you ever been f**king humble in expressing your opinions?"; stick to IMO :) That's what I  do.
  2. IMO, this debate isn't about real risks, it's about passing the inspection.  

I'll have to drop the H then as I always thought it meant "Honest" :S

13 hours ago, ProDave said:

Are they worried you will pee in the bath

Dave, we all know that's a great way of warming the water back up ;) 

13 hours ago, TerryE said:

You might feel that a decent double check valve in the shower feeds should be perfectly adequate, but if you do and this does fail then you would be legally liable for the contamination that occurs

I guess that this statement is now the most important one so far then? 

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18 minutes ago, Nickfromwales said:

I'll have to drop the H then as I always thought it meant "Honest" :S

Dave, we all know that's a great way of warming the water back up ;) 

I guess that this statement is now the most important one so far then? 

  • IMHO. Can be both, but it's just that drop the H after someone got really arsey with me.
  • Doesn't pee feels colder than the bath water?
  • This is true for most actions that you do if they beach some regulation.  However poluting the public water supply is a fairly sure one.  IMO, if I had double check valves on the appliance and on the supply line then the risk of getting killed by lightning is far greater.
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33 minutes ago, Nickfromwales said:

Shall I start a new thread about fitting lightning rods?

 

 

 

( only joking ?). 

:D

 

Please do!  I was involved in some work years ago that looked at their effectiveness in protecting structures (specifically military antenna masts), and I'm sure I've still got a lot of stuff tucked away on both the probability of a strike and the effectiveness (or often ineffectiveness) of lightning protection systems.  I do know for sure that the old adage, "lightning never strikes twice in the same place" is complete cobblers.  There's an antenna farm I know well that has at least three or four strikes every year, sometimes more.

 

(also only joking - I'm certain it would stir up controversy! :D )

Edited by JSHarris
typo - "no" when I meant "know"...........
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7 hours ago, joe90 said:

I have been hit twice by lightening, different houses and were not overly tall ones at that.

 

I think that you mean that your house has been hit by lightening and you yourself not once and not fatally -- unless you are the forum ghost :)

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1 hour ago, TerryE said:

 

I think that you mean that your house has been hit by lightening and you yourself not once and not fatally -- unless you are the forum ghost :)

Yes Terry, you are correct, two houses I have lived in have been hit by lightning whilst I was in them. However I have also been on top of a mountain and seen a guy " hit" by lightning, he was told the reason he survived with no real damage was his rain suit was soaking wet and it carried the current straight to earth, there was black burning from the top of his head down his suit to the ground, he described it as a " fizzing" sensation, I will never forget it.

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A friend of mine was walking one of the coast-paths during the vacation when we were at uni.  A big fizzzt and that was him done for.  A surprising % of people who get hit by lightening survive.  The main reason for death is that their heart stops or goes into fibrillation.  If there's no-one on hand to perform CPR, then that's them gone.  But we'd better stop this diversion otherwise Nick will tell us off :) 

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  • 2 years later...

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