[andysmee]

How about creating an adaptor to go at ground level to plug a drainpipe, in order to use the drainpipe to store water like a water butt.
Given a 15cm diameter pipe, and a 5 metre length (two storeys of a house approximately) you get 88 litres capacity.

All you need to solve is how to allow the system to overflow - perhaps the valve could be sprung to release at high pressure. Hey presto - masses of water storage with no space required. Give it a tap or hose adaptor and you can water the garden. Better still, extend it to feed the ground floor toilets...

Reward: One unit for each drainpipe in my house and I get to name it

[Steve]

I'm not an irrigation expert, but I see several problems with this one: in summer the water would be a breeding place for mosquitos (and in a hot month they could virtually kill you), in winter the water would freeze and most likely ruin the pipe.

There are water tanks though that can be attached to drain pipes. They are somewhat flexible (against the freezing) and can be shut more or less airtight so you don't end up running a mosquito farm.