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USP Purified Water Testing Requirements

The United States Pharmacopeia (USP) is a private company that sets standards for over-the-counter and prescription medications to ensure public health and safety. Not only does the USP create standards for medications in the United States, but more than 130 countries around the world rely on these standards for the health and welfare of their citizens. Among the many requirements it sets are those for purified water that is used in medications, injections and as laboratory animal drinking water.

  1. Microbes

    • A test called "bioburden testing" assesses and analyzes the number of microorganisms present in the water. The test is performed both before and after water purification. The USP considers acceptable levels of mocrobes to be in line with the same levels for purified water established by the Environmental Protection Agency (EPA): 100 colony-forming units per milliliter.

    Chemicals

    • USP standards test purified water for specific chemicals including sulfate, calcium, ammonia, chloride and carbon dioxide. If these chemicals are present, the water is further purified by distillation or reverse osmosis (which is the process of filtering the water through a membrane that catches the containments). Purified water must be free of chemical containments and meet the EPA's primary drinking water regulations. According to the EPA, purified water must contain no more chemical particles than 10 parts per million of all dissolved solids.

    pH

    • The USP monitors water pH only because more acidic water can strip brass and copper plumbing and cause high levels of harmful metals to leach into the water. For water systems with brass and copper components, a pH level of 6.5-8.5 is the standard. For stainless steel or plastic systems, a pH of 2.5-8.5 is acceptable.

    Hardness

    • Hard water can cause calcium carbonate deposits to build up in water systems which can interfere with purity as well as cause functional problems in drinking water systems for laboratory animals. The Langelier Saturation Index (LSI) is a number that is derived from an equation which takes into consideration the alkalinity, the pH of the water, the total dissolved solids, and the calcium hardness. The final number should fall below zero or the water will have a tendency toward developing calcium carbonate deposits.

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