Reservoirification: Why storing water for drinking isn't as straightforward as it may seem

Wimbleball is a water supply facility and it was dug out and built back in 1979 and now supplies drinking water to support around half a million people across East Devon and Somerset.

And gazing across it now, you wouldn't necessarily guess how much water it holds.

It's apparently 21 billion litres.

Unlike a natural lake, a reservoir like this doesn't just fill up with rainwater.

There wouldn't be nearly enough.

So Wimbleball is mostly supplied by water from the River Exe.

but the River Aix is located quite a way below it.

And according to the laws of gravity, water only flows downwards without intervention, so that means the river water has to be pumped up here using powerful engines.

Not all reservoirs need this.

Some, like the Meldham Reservoir up on Dartmoor, can be gravity-fed by streams that flow down to them.

But a lot do need technologies to keep them functioning.

And the way that water gets pumped up here isn't just automatic or consistent.

It only gets pumped up here when it's needed because, of course, pumping water out of a river does have an impact on the river's health and functioning.

You don't want river levels to get too low.

So when the river exit level gets too low, the reservoir operators release water from here back down into the river again.

And that's not only so the river stays healthy, but also so there's enough water in the river to flow into the drinking water treatment plant, which is further downstream.

And we'll explore that in a later episode.

And it's that treated water that travels on towards people's taps.

These waters look lovely and calm, smooth and unruffled, but there's actually a lot going on under the surface.

So hidden in Wimberball's depths is a huge mixer machine, and that can get used if they need to oxygenate the water.

The water quality in this reservoir is constantly monitored for pollutants and other bacteria that can affect drinking water.

And so a lot of action is needed to make sure that the levels and quality remain appropriate.

Given that populations are rising and climate change is increasing the risk of droughts and water shortages, it's commonly agreed that it would be a really good idea to have some more reservoirs created.

But creating a new reservoir is actually a very complex and expensive process and it can face a lot of local and planning hurdles.

And although the UK government is planning 10 new reservoirs at the moment, it's not clear whether they'll materialise or when they'd be completed.