Laboratory-grade water literature is well documented among the large life science water manufacturers. General levels of resistivity, total organic carbon (TOC), particles and bacteria in water classify into Types 1, 2, or 3, with Type 1 having the most stringent requirements. Each type is useful for a different application depending on the procedure:^1,2,3

• Type 3. Generic applications where water will not come into contact with analytes during the procedure
• Type 2. Standard applications such as media and buffers
• Type 1. Critical applications such as GC, MS, HPLC analyzers⁴

Achieving high-quality water requires purification through a polishing step such as deionization (DI), reverse osmosis (RO), ultraviolet light (UV), filtration or distillation, which removes specific impurities.^3,5

This classification system gets muddled, as different agencies have their own standard that examines different end-point analysis and levels:

• ISO (International Organization for Standards)
• CLSI (Clinical and Laboratory Standards Institute)
• ASTM (American Society for Testing & Materials)
• USP (United States Pharmacopoeia)^2,5

With all these standards and testing in place, many labs assume that their installed DI water supply is clean, yet in reality, the water in general would be closer to Type 3 rather than the required Type 1. 

The problem with using lower quality water in food testing labs is that the accuracy and validity of tests will be compromised. Many of the analyzers requiring Type 1 water would recognize contamination from lower quality water, creating difficulty in identifying actual contamination or yielding false positives. False positives can result due to microorganism contamination in the water that is amplified through the testing procedure. In addition, dirty water can damage expensive machinery, because tools in the laboratory that are designed for a high-purity water supply can malfunction when less-pure water is used. For example, a system with microfilters can become rapidly clogged with lower quality water, introducing the possibility of flooding when tubing bursts, if left unnoticed.

Newer regulations in regards to ISO 11133:2014, along with ISO 17025:2005, provide clarity on food microbiology water parameters for the laboratory. ISO 11133:2014 “Microbiology of food, animal feed and water–Preparation, production, storage and performance testing of culture media” describes how water for culture media must be purified. The purification recommended is distilled, demineralized, DI, or RO, and stored in an inert container. To verify purity, labs must regularly test the water to assure microbial contamination is kept to a minimum. Regarding 17025:2005, which refers to food microbiology requirements for accreditation, there should be daily, weekly and monthly testing of the laboratory’s water source to verify required quality for microbiological water. Daily testing examines resistivity of water; monthly testing examines the water’s chlorine levels and aerobic plate counts; yearly testing examines heavy metals in the water. Therefore, accuracy and validity of food test results critically revolve around producing purified water and annual water testing.

Jacob Bowland is Product Manager at Heateflex and Steven Hausle is Vice President of Sales and Marketing at Heateflex.