David Hare-Scott wrote:
The many downpipes is good for conserving water too as it also means you
will harvest all the water in a downpour BUT the system has to be designed
for them to flow into your tanks. The space issue is also difficult but
remember that your tank does not have to be right next to the house as long
as the feed pipes still run downhill to the tank inlet. Long runs of
plastic drain up in the air may be unsightly but you can always put them on
a trellis and grow something over the whole lot.

If you are prepared to pump from your tank then you can bury the tank
somewhere at the lowest end of the house and direct all downpipes to
the tank. If your garden is uphill and you have a single storey house
you might have to do this anyway.

I have considered doing this, maybe have two tanks - one for rainwater
and one for greywater, and share the pump between them.