How to safely link our own spring water with the mains supply

[DavyH]

If you're familiar with the jargon here, then my core question is "what is the WRAS fluid category of my spring water?" But I'll start at the beginning. 😁

 

Our place has a surface spring on the property, and I'm looking at setting up an independent water supply. Recent lab tests show that the water is fine except for a high level of coliform bacteria. People have been drinking from that spring for decades without problems, but fair's fair — I'll UV-sterilise the water. So far so good.

 

Here's my problem: I'd like to keep the mains water connected so I can switch back to it in case the home system ever fails. This means a direct connection between my spring water and the mains. I understand that I need a check valve on the mains side, and the type of check valve depends on the fluid category of the spring water. What's not clear to me is which category my spring water will actually be.

 

I'm hoping I can get away with category 3 (which is roughly "icky, but harmless if diluted"), because a check valve for that is about £50.

 

If I need to take into account a possible failure of the UV steriliser, and raw spring water reaches the check valve? I guess then it'd count as category 4 (which I read as "maybe okay but don't chance it"). At that point it seems you're into much bigger leagues, with "reduced pressure zone" valves costing several hundred quid, and mandatory notifications, yearly inspections and stuff. Still doable, just, maybe...

Or would the presence of any coliform bacteria automatically make it category 5, on a par with raw sewage? Frankly, that'd probably scupper the project.
 

Can anyone give me any guidance on what'd be the right approach here, and what an inspector would be likely to accept?

 

There's a lot of good information on how to handle the individual categories, e.g. a post from @TerryE back in 2017 (Addressing backflow risks in wet/bathroom design), but that seems to be talking about fluids you already know are category 3 or 5 or whatever, and that's where I'm stuck...

[JohnMo]

I would expect a world of issues, without a positive break between the two systems.

 

Assume you also have particulate filters upstream of the UV down to 5 micron, to stop UV filter contamination and effectiveness.

 

Think the only safe way is a 'break to make' transfer, so isolating the spring water first with a removable pipe, which then transfers to mains supply. Mains supply will need a double check valve also upstream of the connection point.

 

I would add a flushing point also to both systems, to get rid of the water which may be stale etc.

 

But overall it's a daft idea.

[Conor]

Why are you ditching the mains water? It'll be more expensive to runs and maintain your own supply.

 

If you want to use your own water, you'll need a properly designed treatment system with backups and failsafes. Check / non-return valves can (will!) fail. So you can't be connected to the public water supply at the same time, unless with an air gap and procedure for flushing and chlorinating. Overall, it's a bad idea. 

Edited November 25 by Conor

[SteamyTea]

1 hour ago, Conor said:

Why are you ditching the mains water? It'll be more expensive to runs and maintain your own supply.

Cornwall has the most expensive water in the country, which makes it one of the most expensive in the world.  By bypassing the meter, sewage charges are reduced if on mains sewage (though that is a bit immoral).

@DavyH

I think that @JohnMo is on the right track.  A totally, unconnected, supply.

Our old mate, Jeremy, who no longer posts, designed his own bore hole filtration system that was a sand filter with ozone injection.  It worked well.

[Omnibuswoman]

My parents have a spring-fed system with UV sterilisation under the kitchen sink. Annual testing keeps an eye on the level of nasties in the water (which are pretty low). Waste water is via a Klargester and soakaway.
Saves a fortune in mains bills. 
When the summer is exceptionally dry it can cause shortages, but not out and out failure of the system. 
Could you not simply rely on the spring and jettison mains?

Edited November 25 by Omnibuswoman

[sharpener]

6 hours ago, DavyH said:

Recent lab tests show that the water is fine except for a high level of coliform bacteria.

 

I have looked into the requirements for this a bit as we have a rainwater harvesting system.

 

I would not let water with known e. coli contamination enter the house. We have UV as a belt-and-braces thing even though (i) there is not routinely any bacterial contamination and (ii) we have a separate mains drinking water supply to the kitchen and wash basins.

 

However in a case like yours IIRC you would be required to have not one but two UV sterilisers with lamp fail detection and automatic changeover on the first failure and shut-off on the second.

 

The water regs are very stringent for a reason and I don't think you would get away with anything less than an air break between the systems as well.

 

If you keep the mains supply you will have to pay standing charges anyway. As @JohnMo says you also need filters upstream of the UV to prevent bacteria hiding behind silt particles. Coupled with UV lamp replacements I would think the consumables and standing charges would make it an uneconomic proposition.

Edited November 25 by sharpener

[DavyH]

Thank you everyone for the input!

 

The most important thing I've learned is that the water people are going to be even more stringent than I thought about not letting anything nasty anywhere near the public supply ever under any circumstances. Which I fully support.

 

As @SteamyTea points out, water is quite pricey here in Cornwall so I won't be abandoning the idea just yet, but I'll assume the mains water and spring water never touch. As they say in Ghostbusters, "Don't cross the streams!"

[SteamyTea]

5 hours ago, DavyH said:

water is quite pricey here in Cornwall

Just about to open my bill and pay it.

[Beau]

I have no idea what's required to comply but as others have said a compete break will hopefully do the trick. Our private supply has a DAB Easy Tank as we lack presure due to lack of head from the spring. The Easy tank is fed with a float valve from the spring. Might it be possible to have a similar system with a second float valve from the mains for when you need it? 

[saveasteading]

1 hour ago, Beau said:

system with a second float valve from the mains for when you need it

Sounds feasible with the mains intake positioned quite low in a header tank and the spring water at the top. Then the spring valve refills as standard and the mains seldom does...the downside being that it will only partly fill the tank.

 

Or modify the float for the mains so that it is low, and underwater most of the time. Big downward bend or extend  the ballcock arm?

[sharpener]

11 hours ago, saveasteading said:

with the mains intake positioned quite low in a header tank

 

You are not allowed to do this as the spring water could conceivably contaminate the mains supply. Yr second idea is better, there are rainwater systems cos that do proprietary versions of that kind of thing e.g. this.

[saveasteading]

11 hours ago, sharpener said:

not allowed

You are right of course. Going to read the link.

We are planning to build a simple diy RWH just for garden watering. A tank inline is easy enough but the pump has to be cheap and cheerful too.

[JohnMo]

On 25/11/2024 at 17:32, DavyH said:

what is the WRAS fluid category of my spring water?" But I'll start at the beginning

Download a copy of G1 and G4 regs and read them. All the info you need is there. And report back.

[DavyH]

11 minutes ago, JohnMo said:

G1 and G4 regs ... And report back.

 

You're a star. That's exactly the kind of pointer that's incredibly helpful. Reading now!

 

Info for anyone else needing the same information in future:

• "Approved Document G" is the Building Regulations section for "Sanitation, hot water safety and water efficiency"
• Short FAQ for the document to get you started: https://assets.publishing.service.gov.uk/media/5a81a884e5274a2e8ab552a5/160321_Part_G_FAQ.pdf
• The document itself: https://assets.publishing.service.gov.uk/media/66f6c6ce3b919067bb4828cc/ADG_with_2024_amendments.pdf
• if those links break in the future, here's a Google search that should pick the documents up: https://www.google.com/search?q=approved+document+g+sanitation+hot+water+safety+and+water+efficiency

Edited November 28 by DavyH

[sharpener]

3 hours ago, saveasteading said:

the pump has to be cheap and cheerful too.

 

Clark brand jet pump from Machine Mart then.

 

With our whole-house RW supply I have had several failures with Stuart Turner and would buy a DAB next time.

[DavyH]

The feedback in the first response on this thread was, "But overall it's a daft idea", and the more I learn, the more I agree! At this point it looks likely that I'll recommend to the house's occupant that they just stay on the mains.

 

On the other hand, I remain fascinated by the topic, so anything else anybody wants to share is of great interest (and possibly even useful to others reading this thread in the future).

 

At this point, my original question (about connecting private and mains water) is toast — yes, I would absolutely not do this. I have seen the light. At a minimum I'd run the mains water to a break tank and repressurise it.

 

I read the G1 and G4 regs, and also the Private Water Supplies (England) Regulations 2016, and in fact the last one was the most educational because it lays out all the risk-assessment, inspection and testing requirements.

 

Open question 1: how much do risk assessments and periodic testing cost in practice for a single-household supply? The Private Water Supplies Regulations laid out a schedule of maximum costs, but this was removed later, and I haven't yet found a description of what the real-world costs look like.

 

Open question 2: does any manufacturer sell an integrated system for fail-safe UV sterilisation and pumping? @sharpener made a good point about redundancy and fail-safe operation (although they appear to be specifically worried about pathogenic E. coli, which isn't likely in our case). I've been shopping around for a do-everything box which both sterilises and pumps the water, and stops pumping if it can't sterilise, so it's guaranteed not to pass untreated water. But I haven't found one, which surprises me because I'd have thought this was an obvious niche in the market.

 

I could make something myself based on (say) a Daro UV Saphir (or two) and some control logic, but it's always a red flag when you find yourself reinventing a solution like that...

 

Edited November 29 by DavyH

[SteamyTea]

Found a man that may be able to help, got the same name and initials as you.  Knows a bit of chemistry.

I shall shout your questions up to him after a leave the nearby Weatherspoons. Be interesting to see what the response is.

 

 

[sharpener]

5 hours ago, DavyH said:

although they appear to be specifically worried about pathogenic E. coli, which isn't likely in our case

 

I am having difficult reconciling this statement with the following

 

On 25/11/2024 at 17:32, DavyH said:

the water is fine except for a high level of coliform bacteria

 

 

 

5 hours ago, DavyH said:

Open question 1: how much do risk assessments and periodic testing cost in practice for a single-household supply?

 

Expect to pay three figures p.a. It cost me ~£150 to get a full analysis done, they found high Fe concentration but couldn't advise why it might be there or what to do about it. Also paid a specialist firm who supplied bone char filters and pH correction media, they weren't very impressive either.

 

Simplex Health have a range of DIY tests (but their pH strips are no good with low conductivity water, use the drops from Water for Health instead).

 

5 hours ago, DavyH said:

I've been shopping around for a do-everything box which both sterilises and pumps the water, and stops pumping if it can't sterilise, so it's guaranteed not to pass untreated water. But I haven't found one, which surprises me because I'd have thought this was an obvious niche in the market.

 

Companies like Wrekin Water can advise on a complete system and supply the bits, they were quite helpful in advising on pH correction.

 

It looks as though you could get the Daro steriliser with voltage-free output and use that to control yr pump, would at most require a relay or small contactor. Possibly with a solenoid valve as well to ensure positive shut-off if lamp fails. Try them, IME talking to the equipment suppliers is more useful that trying to find specialist services.

[DavyH]

8 minutes ago, sharpener said:

I am having difficult reconciling this statement with the following

 

This comes bracketed with a heavy disclaimer of "I am not an expert and you have my permission to laugh if I die of enteritis", but I've consistently read that coliform bacteria are a huge class, of which the vast majority are harmless and fairly ubiquitous in soil and surface water, which our spring is. Most coliform bacteria aren't E. coli, and even most E. coli aren't pathogenic. You test and treat for any coliforms because it's a quick cheap test and a safe approach — if you've got no coliforms then you've got no problem. I thought Coliform Bacteria in Drinking Water was a nice explanation, if you don't mind translating from the American.

 

Obviously if there was any chance the coliforms were from human crap, I'd be radically more strict about this, but there's no human presence anywhere uphill from the spring. The water filters in through subsoil and collects some blown leaf-litter (we might enclose it), so it's pretty much inevitable that there'll be some coliforms in it, without necessarily being any health risk. There's a certain amount of sheepshit on the fields uphill, but I admit to being fairly blasé about that after the water's filtered through umpteen metres of ground.

 

I'm still in favour of sterilising it though! My point is just that the presence of coliforms doesn't per se make it a health risk, any more than the presence of Cornish people in your house means you're about to be abducted and used for pasty meat. You just exclude them on principle as a sensible safety measure in case any of them are from Camborne.

[sharpener]

If there are coliform bacteria present I would also worry about possible cryptosporidium from animal faeces, this has cost SWW a shed load of money this summer in an area near me.