Other things, such as sawing metallics or pushing too hard, will have a negative impact on blade life. Let the diamonds do the work, don't force your material through the blade. Diamonds are not good for cutting most metals. On hard stones, oil is best. Next best is LUBE COOL 4800 mixed per label directions.
Water is a poor third place.
Water has no lubricating properties. This will lead to reduced cutting life of the blade. Water can also cause poor bearing life due to lack of lubrication and rust. For soft stones, water is a satisfactory coolant. However, just water can cause rust and bearing problems.