New homeowner: what is this huge water tank for?

[david.hollman]

Not quite a DIY question but this seemed like the right group of people to ask.

So in my loft there is an enormous water tank. I'd guess, 200 litres?

500? Its big.

(It is not the radiator tank AFAIK that is a smaller one)

It seems that this is a reservoir for tap water. The bathroom is upstairs (first floor). The tub has MUCH higher pressure than the sink, so I assume the former is mains and the latter is the tank. FYI the garden hose produced reasonable pressure at about the same height when I was washing moss off the roof of the extension hence my assumption.

Anyway, the question is, what is this huge tank for? If mains pressure is good enough... why bother having it?

And is it sanitary? I suspect I'm missing out on some important homeowner duties in terms of caring for this thing.

Thanks, David

[Grunff]

Traditional vented hot water systems use a loft tank to feed the hot water cylinder. So the water in that tank provides the head for your hot water in the bathroom and kitchen.

In order to get similar flow rates from hot and cold taps, and in order for shower mixers to function correctly, the bathroom cold taps and shower are usually also fed from this tank.

It should have a well fitted lid, and the water in it should be clean.

[Andy Hall]

200 would be fairly large but not impossible.

It's the cold supply for the hot water system.

Because the mains may not be able to deliver the flow rate.

Yes, provided that it has a cover and a water byelaws kit. That consists of various screens and bits for the various pipes to keep creepy crawlies out.

[John]

I would presume (without looking at it) that it is the feed tank for your immersion cylinder which you will probably find in an upstairs cupboard, although they can be downstairs in certain installations. To check look for an immersion heater cylinder or sit next to the huge tank and ask somebody to turn a hot tap on and you should hear it refilling. Unless of course you now have a combi boiler and the lazy ar**d plumber couldn't be bothered to empty and remove this tank!!

HTH

John

[Lurch]

On Thu, 5 Jul 2007 00:27:01 +0100, "John" mused:

It's not an immersion tank\cylinder, it's a hot water cylinder.

[Dave Baker]

If you find the stopcock supplying mains water to your house and turn it off then any tap that still works is supplied from the tank.

FYI

It's called a "spider tank". Its primary purpose is to supply the head for the hot water cylinder and the non-potable cold water supplies in the bathrooms. Its secondary purpose is to give spiders in your loft somewhere to live, spin their webs and eventually grow huge, die, fall into it and decompose. From time you therefore run a bath and find enormous chitinous chunks of legs and carapaces swirling about in the water. Doesn't bother me much but puts the fear of god into female guests :)

Of course you could put a lid on it I suppose but that would spoil the fun.

Does anyone else keep a plastic sieve hanging on a nail by their bath or is it just me? OK, just me then. Thought so.

[Lobster]

Note that not all homes have them; mine doesn't, for example. It's a very 'British' thing. I think there's a move away from fitting them these days.

You'll find that that it won't be connected to the kitchen sink (and possibly others?) - if so that's the only tap which should be used for drinking water.

David

[Brian Sharrock]

Two comments; - the 'British thing' about having a tank of water in the loft relieves the requirement for the main to 'instantly' supply the water used ... generally smoothing out the flow on the main- the tank-in-th-loft acts as a capacitor - AND if the main is subject to 'problems' such as a burst (bomb or accidental) then there's a supply of in-house water to flush the toilets etc. [This used to be called 'Civil Defence' but it's nowadays called 'Resilience Preparedness']

[John]

As others have said, it's almost certainly a header tank for your hot water system.

Modern requirements are for a tank to have a close fitting lid, insect traps on any breathers and the volume should not exceed 24 hours normal usage. What is it made of and what's the condition of the tank and the water? If there's rubbish/rust/scale in there, you should do something about it. Google Legionella L8 for more info. L8 is the HSE Approved Code of Practice and, although it doesn't legally apply to domestic houses, is a good basis for your decisions.

John

[Peter Ashby]

I discovered a couple of years ago when the lockshield failed to work that our toilet is mains fed*. Which meant I could work on the sistern and them who wished to use the toilet could flush it via a bucket filled from the bath, which is on the header tank. Worked long enough for me to learn compression fitted plumbing ;-)

*After I had bought one of them rubber bung on a string kits for shutting off the header, assuming the toilet to be on it.

Peter

[Dave Plowman (News)]

Depending on the water system design, it might supply all the water to the house with the exception of the kitchen cold water tap which is always mains.

The problem with mains everywhere can be not the pressure but the maximum flow. So that flushing a toilet might effect the operation of a shower, etc. With a well designed storage system this doesn't happen.

A storage system relies on evening out demand on the mains input - it obviously can't supply any more water over a period than the mains can supply. But is capable of allowing much greater peak demands, and replenishing itself at quiet periods.

These days most would want mains cold water where it is likely to be used as drinking water etc. So to bathroom basins etc as well as the kitchen. Although stored cold water will be perfectly safe to drink if the storage tank complies to regulations.

[Dave Plowman (News)]

Are there any documented cases of Legionella causing problems in a domestic storage system?

[John]

The easy answer is no but as domestic properties are not investigated, no one knows the extent of the problem. There are certainly cases where people have contracted Legionaires disease from showers.

disease is a respiratory infection similar to Pneumonia. It's contracted by inhaling a contaminated water aerosol. The most likely sources are cooling towers and spa pools but there are many others. Basically, if you keep water for longer than a week (less if it's warmer) Legionella bacteria will almost certainly develop. If that water is then sprayed, an aerosol is produced which can cause Legionaires disease. Most UK cases arrise after holidays, particularly foreign ones. In warmer climates, Legionella is more difficult to control and, with an incubation period of 7 - 10 days, any illness could occur long after the holiday. Coincedentally, during the holiday, the domestic water system is unused. Loft tanks etc get warm and the bacteria grows. Run a tap, flush a toilet, spray water on the garden or have a shower and an aerosol is produced. By the time any symptoms develop, the house sytem has been flushed many times making detection difficult. There's lots of information out there if you're bored.

John

[Dave Plowman (News)]

led to contamination of a water supply.

I'm more concerned with a domestic storage system. Many seem to think them unhygienic - and I wondered if there was any substance to this rather than purely a 'gut' feeling. After all, they were the norm once in many areas - and with open topped tanks.

[Tony Williams]

When we lived in Cheltenham the next door had two young children. Their hot water supply had always been a little erratic, but when she was filling the bath one evening for the two girls the decomposed remains of a large bird came through the tap.

The tank in the loft had no lid and they think that a blackbird or starling had fallen in, drowned, rotted, and eventually bits of it came through the pipes.

She still has the heeby-jeebies about exactly what they were bathing in all those months before.

[EricP]

Many years ago I did read an article on this and the tanks were a breeding ground for bacteria, not necessarily harmful ones. Much greater emphasis was put on vermin dying in them.

The bacteria angle was because the tanks tended to be galvanised and right over the airing cupboard for the support of the four cupboard walls, and thus warmer than expected for a roof situation. Also the tanks tended to be large, having to supply all internal water, except the kitchen tap, and thus only partially emptied with daily use.

The tanks were run from solid fuel back boilers and subject to the overheating pipe emptying into them for additional hazard, there being no dedicated CH header tank.

As another poster said rules were tightnened with close lids and capacity only to supply a daily need to ensure regular water changes.

We sold a house at Xmas with exactly this situation and I always shuddered when I cleaned my teeth there, remembering where the hot and cold water to the basin was coming from.

[John]

As I said, since domestic systems are rarely checked, information is very sparse. However, we carry out routine water tests at work and recently found Legionella in 3 of our hot water cylinders so it's more than just a theory. Our systems are larger than domestic but of a similar design.

Open topped tanks are essentially unhygenic as others have said. The longer that the water is in there, the worse it gets. That's why tanks need to be as small as possible to reduce the residesnce time. They should also be as clean as possible so that the water (and bugs) can't hide and stay for long periods. Tanks should also have the inlet and outlet at oposite ends to prevent stagnation. All very simple things that can make a water sytem much safer.

John

[Lobster]

Mm, nice... hope it didn't feed the bathroom basin tap too!

David

[nightjar]

Current thinking is that contaminated water in the mouth aspirated during choking or coughing is the primary method of infection and possibly was even the way the outbreak that gave the disease its name happened. That means that any stored water system presents a potential risk and is a good reason for having the handbasin in the bathroom mains fed, to reduce the risk to anyone cleaning their teeth there. Mind you, I make and sell water byelaw kits, mostly for really big systems (an 8" overflow pipe is the largest so far), and my loft cistern is still unprotected - the cobbler's children syndrome.

Colin Bignell

[Tony Williams]

So do I, but knowing that builder..........