Thor, or should that be Zeus?

[m_c]

I'm thinking of different ways of doing the WC on the new machine under construction. Maybe a filter and maybe pumps / valves arranged so the water is emptied back into the reservoir at the end of a session leaving the spindle dry. Someone will probably tell me that it will be worse if it dries out . . .

It will be until it completely dries out.
Far simpler option is to put some anti-freeze (or summer coolant) in, as it has corrosion inhibitors in, and will improve the cooling performance over plain water.