Private water supplies running dry as bed numbers outgrow the pipes

Eleven private water supplies in the north west ran dry or fell below usable pressure during July, in a month with rainfall close to the long-term average.

Private supplies — springs, boreholes and hill catchments outside the public network — serve around 3% of Scottish households, concentrated almost entirely in the areas where visitor accommodation has grown fastest.

The supplies are not failing because of drought. They are failing because of arithmetic.

The arithmetic

One catchment surveyed for this article was assessed in 1978 for a settlement of ninety residents. It now serves the same ninety residents plus 4,100 visitor bed-spaces added within its boundary over twelve years, each of which has, on average, a shower.

Peak summer draw exceeds the assessed yield by a factor the hydrologist involved described as “not marginal”.

“Nobody did anything wrong. Every one of those conversions was approved on its own merits. There were four hundred separate decisions and not one of them was about the spring.”

A hydrologist working on rural supplies

The other end

The corresponding problem is disposal. Septic tanks sized for a family of four are serving properties sleeping twelve, and the discharge consents attached to them were issued on the original basis.

Regulators have reported a rise in complaints about watercourse contamination in areas with high short-let density, though establishing which tank is responsible in a glen with sixty of them is slow and frequently inconclusive.

The fix nobody has proposed

Every expert consulted gave the same answer, and it is neither expensive nor interesting: make catchment capacity a material consideration in change-of-use applications, and require an updated discharge assessment when sleeping capacity increases.

Neither is currently required anywhere in Scotland.