News that the first major new reservoir built to bolster domestic water supplies in England since the 1980s is to be constructed near Havant in Hampshire may make a few people across the south-east of England curious about where their water is coming from. 

Portsmouth Water and Southern Water have jointly commissioned the new reservoir at Havant Thicket, which is the first in the south-east to be built since the 1970s. A key purpose of this new supply will be to reduce the amounts extracted from chalk streams nearby, such as the River Test and River Itchen, which both flow through Hampshire to Southampton.

Using chalk streams to supply water is not just a potential problem for the ecosystems of the watercourses themselves. By definition, these streams flow down from the chalk downland that dominates much of southern England and is therefore infused with calcium, which leads to hard water.

Anyone using water softeners in High Wycombe will do so because this is also the situation faced by Buckinghamshire households and is indeed why, if you don’t have such a filter, it makes sense to get one. 

As Buckinghamshire Live noted in 2021, 85 per cent of the world’s chalk streams are in England and the highest concentration is in the county. This situation will not have changed since then precisely because there are no new alternatives such as a freshly-built reservoir. 

The proportion of water sourced from reservoirs or from rivers and streams varies all over Britain, although more northern areas get naturally softer water, both because there is less calcium in the ground and because uplands like the Pennines, Lake District and the mountains of Scotland and Wales create bigger potential catchment areas for reservoirs.

In addition, much of the water in the south comes from the chalk aquifers themselves, adding further to the calcium content of water and thus contributing to its hardness. Indeed, Southern Water presently takes 70 per cent of its water from this source, with 23 per cent from rivers and streams and just seven per cent from reservoirs.