There are ways to "soften" the water and get out a lot of the solids/minerals, but I don't keep water turtles and I don't know what to tell you.
Maybe someone else can help with that.
The easiest way would be to use bottled water, but that wouldn't be very economical.
Mr ZERO is the winner!
I'd also like to add it may be the 'seams' right along where the turtles will shed it's scutes. They'll usually peel up a bit before coming off.