Water composes more than 95% of in-use metalworking lubricant. It therefore makes sense for the water quality to affect the performance of the coolant and therefore parts quality.
Several water-related factors such as hardness, chlorides, acidity, conductivity, bacteria and fungus can be examined for their effects.
Water used for metal working should have a hardness of below 150 polyvalent metal ion parts per million. If the water is too hard, corrosion and emulsion splitting will occur. If the water is too hard, the fluid will foam.
Evaporation occurs during machining because of friction and heat from various sources. This evaporation can concentrate mineral content, especially as more water is added to the sump to make up for the evaporation. The water hardness will therefore increase. To reduce hardness, water softeners, ion exchange cartridges, de-ionizing units and boiler condensates can be used.
High levels of chlorides can also lead to corrosion. Chlorides are used in treating water to prevent bacterial and algal growth, but they are also found in well water. It is also possible for malfunctioning water treatment equipment to introduce chloride contamination into the liquid.
Extremely acidic or alkaline water should be treated until it is neutral at a pH of 7. Water with pH values between 6 to 8 is suitable for machining use.
Water conductivity should be below 500 micromhos. High measurements mean there are high salt levels in the liquid. These need to be treated or discarded.
Water from ponds or lakes tend to have large amounts of bacteria and fungus. These feed on metalworking fluid and grow quickly if they are not eradicated by treatment before use.