Never use just water as a coolant. You may not want to use oil either. An alternative is Intricate 410, an additive to be used with water that we sell for $24.50 a gallon, plus freight. Used mixed with water in the ratio of one part to 20 parts water it provides an anti-rusting coating on metals as well as better lubrication. The detergent ingredients do not break down with time or use so that this can be used for longer periods than the biodegradable products available from machine supply companies.