In article ,
Stephen Wolstenholme wrote:

When it's not Winter most rainwater that falls evaporates before it
gets into reservoirs even when there isn't much Sun.

That is an oversimplification, bordering on a falsehood. It is
true for the driest parts of the country, but assuredly not for
the country as a whole. In the wetter parts, evaporation never
exceeds precipitation, on average.

The average evaporation in the UK is about 11", almost all in
summer, and the average rainfall varies from 19" to 40+" in the
populated areas (and a LOT more in a few places).


Regards,
Nick Maclaren.