Water meth used on the big piston engines too. Tap water is ok, meth just to stop the water freezing and some fish oil to lube the pumps and diaphragms ,etc.
R2800 radials on the DC-6 use it to boost take off power. Makes a top noise when 'full wet power' used.
RR Dart water meth is highly carconagenic. When I was with JEA on the F27's, it could only be topped up in Jersey, not on the mainland. Says a lot.