By Hank
Cheshire,
United Kingdom 
Thanks to all who replied ( ground water)
I've been so busy I've only just remembered to look at your answers to my question dated 9 th Jan.
Thanks Urbanite for your input, but the water level is only low because I bale the damn thing out every day - even though my son insists I'm wasting my time.
And thanks to all who replied, I'll sort it out.
15 Jan, 2016
Answers
O.M.G. I hope not ! But I forgot - there has been some rain - every damn day ! ( except today so far).
16 Jan, 2016
Previous question
« have taken cuttingsand they have taken but are lookingspindle
If you bale it out every day even when there is no rain, it might be a small artesian spring.
15 Jan, 2016