Rainwater harvesting, where water from gutters of roofs is collected to a single point and stored for watering gardens and flushing WCs, is both strongly encouraged and increasingly popular. Such systems both reduce the amount of clean water drawn from the system, and reduce the pressure upon storm drains which may otherwise overflow and flood.

The usual way of doing this is to site the storage tank below ground, simply because it’s out of the way, it is easy to redirect gutter pipes to it and the weight of the full tank will not be an issue. Usually a pump is fitted in the tank and pumps the water to wherever it’s needed.

You could site your storage tank in your loft, but be careful of several things. First, you must ensure the tank is supported on sufficiently strong structure to bear the weight of the tank when full of water. If your tank is to be big enough to be meaningful, this will be substantial and you may need an engineer to calculate your loads.

The next problem with siting your storage tank in the loft is that generally the gutters of a roof will be below the level of the top of your tank, so you will have to collect the water below and pump it up to the loft. This means that you may be better siting the storage tank lower down, or undergroubd, anyway.

I have 800 liters of storage capacity for rain and ‘grey’ water beneath a flowerbed in my garden. I doubt that I would have had either the space or sufficient support in my loft for such capacity, but beneath a flower bed I can forget all about it.