Town Water supply - vulnerable to disease if water not cold?

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OldGeek

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#271667 21-May-2020 12:43

My wife and I have recently moved into a new home and discovered that the main (town supply) water pipe from the boundary to the house is mostly just sitting on the ground - although about half of it has been gradually covered with the residue of garden waste and compost etc. On a sunny day our cold water runs warm because the other half (around 40 meters) is exposed to sunlight in a very shallow trench. My section is 3000 M3. The local authority describes the water supply as 'treated' so probably chlorinated and possibly fluoridated.

I had a plumber look at this. He advised that the heated water is at risk of contamination with Legionnaires disease.

He has quoted me to bury the pipe to 300mm+. Can anyone comment on said contamination risk?

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PolicyGuy

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#2488685 21-May-2020 13:00

First, check what your local authority means when it says the water is "treated".

From the point of view of health concerns, chlorination would be the important factor, in my entirely uninformed opinion. That's because the chlorination should continue to kill 'nasties' after the treatment point, whereas other treatments such as UV irradiation only kill at the point of treatment.

If your town water is chlorinated, then I'd say your health risk from your shallow / unburied supply pipe would be between very low and negligible.
If your town water supply is not chlorinated, I'd guess your risk to be between moderate and low.

I would be at least a bit worried about the water supply pipe being pierced or broken by over enthusiastic fork or mower use if it's on the surface or just under it.

Without knowing the terrain or your capabilities, maybe you could hire a Ditch Witch (or equiv) and dig the trench yourself?
Or get a general contractor rather than a plumber - the plumber will probably be subbing the trenching anyway?

OldGeek

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#2488688 21-May-2020 13:10

PolicyGuy:

First, check what your local authority means when it says the water is "treated".

I am not in a metro area. The website says no more - it is more about consents and connections than defining how water is treated. I am inclined to bury the pipe so not inclined to investigate further.

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MikeAqua

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#2488690 21-May-2020 13:15

Heat is not a contamination risk, it is a proliferation risk. The correct temperature would encourage legionella to multiply. I'm guessing this would be in the range of 20C - 40C, but I don't know for sure.

But the bacteria has to be there in the first place for that to happen. Legionella would only be present if treatment is inadequate or it can somehow get into the pipe system after treatment.

Mike

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#2488734 21-May-2020 14:13

I'd bury it, personally. Gets it out of the way if nothing else.

francisbaud

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#2493340 28-May-2020 08:50

As others have said, burying it seems like the simplest thing to do. Also knowing if the water is chlorinated would be important I believe. However I'm not an expert so take this advice with a pinch of salt.

francisbaud

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#2493341 28-May-2020 08:50

*double post, sorry!*

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boosacnoodle

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#2493353 28-May-2020 09:13

I would bury it just for comfort. If you're concerned about water quality / safety, there are various filters you can get get of varying cost & complexity with different features.

tripper1000

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#2493438 28-May-2020 10:31

It is fairly well know that having a hot water cylinder temp set too low can be a problem, like this case in New Zealand. I've never heard of it in above ground plumbing though.

It breeds in slow moving/stagnate water and your pipe would have water flowing in it too regularly and quickly to give germs time to multiply. In the above article it talks about solar hot water systems having to reach 60 deg once per week to keep legionnaires away, and there is no way you incoming water pipe will be static for that length of time.

Bung

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#2493440 28-May-2020 10:32

I'm surprised you describe it as just warm. I could shower under the water in our 20m garden hose until it runs cold.

I can't find it now (all references to temperature seem to relate to hot supply) but I think there was a requrement when running hot and cold pipes to avoid heat transfer to the cold supply.

Surface runs seem allowed so long as the pipe is UV protected altthough Wellington has 100s of connections with just the blue pipe. The options for depth seem to be 600mm or 450mm under garden areas. 300 seems a Chorus approach.

linw

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#2493702 28-May-2020 14:46

We have the cold water feed coming through our ceiling space and it gets quite warm in summer. This is in a retirement village so I would assume that this affects about 100 villas from 10 to 13 years old. If it was a problem, I guess it would have surfaced by now.

Can't say I am worried but I can understand the OP wanting the pipe buried.

tripper1000

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#2493726 28-May-2020 15:26

There are other good reasons to bury the pipe - such as mechanical protection. Pipes & wires above ground tend to get squashed by cars and hit by weed wackers and mowers. It's poor trade practise to attach them to fences etc.