Built originally to supply Tee-sides heavy steel industry with fresh water ( there is an underground pipe). At the time there was an amazing uproar to flood several areas of beauty plus a few homes to build it. Northumbria Water have a stunning time lapse video of the original project.
When the steel industry waned, then it became a tourist destination as sole use.
Kielder is also why we here in North East will never need to worry about a drought. Ample supplies in reservoir.