As soon as the water sample has been collected, some of the chemical characteristics of the water start to change. For this reason some samples must be preserved to keep the quality of the water sample as stable as possible until the analysis can be carried out. It must be kept in mind that the preservation technique only retards chemical and biological changes that continue after sample collection and will not stop quality changes altogether.
- It is important to keep the samples as cool as possible, without freezing them. In general, the shorter the time between collection of a sample and its analysis, the more reliable the results.
- Preferably pack water samples in crushed or cubed ice during transportation (only applicable if samples will be delivered to the lab within 6 hours as the ice will melt after longer periods). This specifically applies to microbiological and nutrient samples.
- Avoid using dry ice as it will freeze the samples and may cause glass containers to break. Dry ice may also effect a pH change in samples.
- Chemical samples should be kept cool and analysed at a lab within 7 days of sampling. This excludes the physical measurements (eg pH) that are taken on site, and microbiological samples that must be analysed within 6 hours of sampling if not cooled and within 24 hours if cooled.
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