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You can make a sand filter out of a piece of plastic tube, dustbin, etc.


Sounds like a good idea!
Would I keep the rainwater going through it all the time?

You don't have to, but it wouldn't harm it, and might help to keep it
clear. (I'm thinking of soap scum - it'll thrive on skin fragments)

This is similar to the sort of filter used in a waterworks. Back in the
time when Scouts were Boy Scouts and wore big hats and shorts I helped
with a Senior Scout County Venture weekend camp. Part of the
'entertainment' was a lecture and demo by a boffin from the water board,
and he brought along two plastic oil drums and some bags of sand, gravel
and stones.

He asked me and another to find the filthiest water we could and bring a
bucket of it back.

I looked at him, and he looked at me, and evil grins spread across our
faces, for on the walk down to the site we'd both noticed a ditch
outside a farmyard, and the water in it looked and smetl *EVIL*.

We brought back a bucket of this stuff expecting it to be rejected as a
health-hazard, as we'd been promised a drinkable result. Not a bit of
it! he went into raptures, extolling it as the filthiest water he'd ever
seen. He put some in a glass, and it was green, a horrible pea-green,
and when he held it up against the light it looked red.

Passed through the filter, it came out a sandy colour, but passed
through again, it was clear and bright, but not drinkable, as you needed
a fortnight or so for the (natural) algae to build up and coat the
stones and sand grains. So, he added some Milton, swirled it round a bit
and took a swig. He passed the glass round the hundred or so Scouts, and
a few of us tried it.

I'm still here...

You'd need to collect the water and either pass it through a 'closed'
filter, or if you have an open top, to arrange header room and have a
ballcock to prevent it overflowing.

Would I need to clean this out periodically, or would it keep it's self
clean!?

I intend having two parallel filters, and be using one until it needs
cleaning (which may be never, I don't know), and then switch to the
other.

(I would filter out the big bits of crap from the roof with my current
filter)

Well, yes. I'm sure the waterworks does that, too.

I've used a similar filter, pre-packed and pre-charged with algae in a
piece of plastic drainpipe to filter some slightly murky stream-water at
a camp. It passed through the filter fairly slowly, but we just left it
trickling into the receiver, and the water was sweet and clear when we
came to use it.

--
Rusty
Open the creaking gate to make a horrid.squeak, then lower the foobar.
http://www.users.zetnet.co.uk/hi-fi/