442 Natural Water™ Standard Solutionis used in calibrating many Myron L®Instruments. It is the best choice when measuring boiler and cooling water samples, city water supply, lakes, wells, etc. “442” refers to the combination of salts mixed with deionized water to comprise this standard: 40% sodium sulfate, 40% sodium bicarbonate, 20% sodium chloride. A combination of standard salts is necessary since natural water salt type and concentration can vary greatly by location. After much research, the 442 Standard was developed by the Myron L® Company more than 40 years ago. It remains the world’s most accepted standard.