Hi Brightlight
sorry to hear your having this problem.
Had my share of spongy skin moments but ok at present on my current regime.
I've started eating more bananas
I drink both tea and coffee as recent reports have squashed the myth they are worse than taking water.
As long as your total liquid for the day meets the guides or what your comfortable with then go with it.
Have a day every so often and just have water.
Only thing I notice is that I pee more regularly when I'm on tea (diuretic properties but not to the point it would cause a problem).
There are chemical diuretics sold over the counter or you can get docs to prescribe.
However they drain the body's store of potassium and tend to flush out more calcium.
This could lead to more risk of osteoporosis in the longer term.
One thing I do notice though on days I stick to water on its own, I tend to be running to the loo more often
Hope that helps