Rainwater tank as feed for internal sink - practical?

[Bert Coules]

A notion occurred to me today for my detached garage-workshop conversion. It would be useful to have a small sink with a cold water supply tucked away in one corner, but I can't run a proper water feed to it from the incoming main (or anywhere else in the house). As it would only be for occasional and limited (and non-drinking) use, would it be practical to set up a roof-level rainwater tank and take a supply from that? The tank could have an overflow to the same water butt that's currently fed from the garage's gutter. In dry spells it would be easy enough to top up the tank from a hosepipe if necessary.

Obviously, the output from the tank would need to be filtered, and that's where I see a possible snag. Wouldn't any filter get clogged rather quickly? A filter in the tank would be pretty inaccessible, but perhaps something cold be rigged up in the supply pipe? And perhaps a mesh covering over the top of the tank would help?

Maybe this or something like it standard practice in these eco-conscious days and I'm asking the obvious. Apologies if so, but any thoughts will be very welcome. Thanks.

Bert

[Bert Coules]

I've now had a quick look round at existing systems and as I suspected there are some very sophisticated (and pricey) arrangements possible. What I'm considering is something far more basic: no underground storage, no pumping, no complex distribution, just a single cold-water feed directly down to a small sink. If the filtering can be made to work on such a small scale, it seems a feasible proposition.

Bert

[Hugh - Was Invisible]

You would need to drain and close it off in winter or keep it warm

[Andrew Gabriel]

I don't think so. I don't filter the water from my water butt, and it always looks very clear. Muck either floats on the top, or sinks to the bottom. Make sure your take-off is above the bottom. You might also want to plumb in a separate bottom drain so you can easily flush out the tank once in a while. I often have a bucket of water which I've filled from the water butt, and I see the local cats and foxes regularly drinking it, so it can't be too bad. I also run the pressure washer from the butt for cleaning the car and other things, and that's been going fine now for over 10 years.

Use a tank with close fitting lid, as normally used for cold water storage, unless the want the place swarming with mosquitos. Might want to arrange so the overflow skims off the surface muck (they usually aren't arranged like this in header tanks).

You'll also want a tap which operates on very low pressure, and you probably want to run the pipework in 22mm for as much of the way as you can. That may also help prevent freezing, but you'll need to lag the pipework, and the thicker the lagging, the longer a cold spell it will survive. Don't forget the tank too, although that's just as much to prevent excess heating in the summer.

I keep thinking about doing something like this for toilet flushing.

[Nightjar]

Look at Koi pond filtration systems for an idea of how to filter the water. The most important, for your purposes, would probably be to have a first stage vortex filter. A series of over and under baffles after that should remove most, if not all, of the solid debris.

Unless you like green water, the storage cistern should be light proof. You would probably also want to keep insects out with a Byelaw 30 kit - a screened air vent and an insect screen in the overflow pipe.

Commercial water harvesting systems are available, but they tend to be a bit pricey.

Colin Bignell

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Bert Coules" saying something like:

Occasionally I service a boiler in a church that has no mains water - it being fed from a tank filled from the guttering. I'm always bloody careful to disinfect my hands after washing them there.

[AnthonyL]

In the tropics I had a house which used rainwater from the roof for everything. A thin layer of kerosene/paraffin dealt with the mosquito issue.

[Bert Coules]

Thanks to everyone for the replies and thoughts. I've done a bit of reading round on this and it does seem to be a practical proposition, though my initial idea of simply having a free-standing tank to catch direct rainwater fall doesn't seem to be the popular way to go: most harvesting systems, even small-scale ones, appear to work by collecting run-off from roofs.

I didn't know about the existence of low-pressure taps, so particular thanks to Andrew for that bit of info.

I've also found this:

- a low-cost self-operating downpipe filter to get rid of leaves and other debris - which might be useful.

Bert