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'No-water' hydropower turns England's hills into green and pleasant batteries
(www.rechargenews.com)
This is a most excellent place for technology news and articles.
If the fluid is what I'm thinking it is (calcium carbonate in water with a stabilizer), fluid loss would just be water loss and they wouldn't go to great pains to isolate it. They'd just add more water, since most of the weight they're pumping is the calcium carbonate.