There is no water shortage. What we have in this country is a storage shortage, probably because we never imagined we would run out of rain.  

  Water butts are a good idea -to a limited extent. This one holds up to 100 litres and is fed by the downpipe from a pitched roof approximately 6.5m long by 5m wide which is 35.75 square metres. Given the average rainfall in the region that roof will receive over 23,000 litres of water per annum! [the formula is 1 litre of water per square metre per mm of rain x average annual rainfall in mm]

 In fact I didn't rig this one up for storage; rather it collects the water from the roof to distribute round the garden. The tap with hose is always on so the water goes straight onto the garden (better that than down the drain into the sewer system). In an intense rainstorm it sometimes fills up faster than it empties so there is also an overflow hose at the top.

 100 litres is only 10-20 watering cans, a drop in the ocean so to speak. If we want to (or have to) get serious about water storage 1000 litres is probably the bare minimum. Even then a hosepipe would drain a full tank in an hour or so. That's ok if the tank is being topped up by regular rain but won't last long through a drought summer like this one.