Much of what's stored in Bewl Water is pumped from the upper Medway catchment, where it's been drier, and normally pumping is confined to the winter months anyway.
https://wikishire.co.uk/wiki/Bewl_Water
And ...
The catchment area of Bewl Water is 2077.5 hectares (20.775 square kilometers) according to Data.gov.uk. This is the area of land that drains into the reservoir. The surface area of the reservoir itself is 309 hectares (3.09 square kilometers) according to the UK Lakes Portal. If every drop of water went into the reservoir, a foot of rain would raise Bewl by six feet; I should think it's less than half that in summer conditions when rain gets intercepted by vegetation.
I did a crude experiment when I was teaching A level Geography to check a text book statement that it took half an inch of rain in high summer before significant quantities reached the ground, being intercepted by leaves (and some of that would be taken up by vegetation growth). I thought that seemed an over estimate, but the experiment suggested it was about right.
The experiment consisted of assembling a pile of vegetation on a plastic sheet, and getting a sixth former on a step ladder to pour water onto the pile from a watering can.😂😂
Originally Posted by: DEW