Definition
Water that has been sterilised and contains no preservative, used as a diluent for single-use preparations.
Sterile water for laboratory use is purified water that has been sterilised, typically by filtration or autoclaving, and sealed to remain free of viable microorganisms. Unlike bacteriostatic water, it contains no preservative, so once a vial is opened it offers no protection against contamination introduced later. It is the usual choice for single-use preparations and for assays where preservatives such as benzyl alcohol could interfere, including many cell culture experiments. Sterile water is not necessarily endotoxin-free, so endotoxin-sensitive work calls for water specified as low-endotoxin or pyrogen-free. Because pure water has no buffering capacity, some peptides dissolve poorly in it and need a dilute acid or base first.