Distilled Water

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Distilled water is water that is purified by a procedure called distilling. This Distillation is performed in order to purify laboratory water for use in various tests. Since many organic molecules have vapor pressures that are higher than water's vapor pressure it is possible that distilling water will not completely remove impurities in a water source. If you are having problems with BOD it is possible that you will have problems with contamination even though the water is distilled.


  • If there is a reservoir for the water system, inspect the reservoir for signs of microbiological growth. If there is any evidence of microbe growth, clean the reservoir. Even if there is no sign of growth consider cleaning the reservoir.
  • Obtain another distilled water - for example from a grocery store or perhaps another laboratory. Try blanks with this water in place of the distilled water that you currently use. If there is improvement in the blanks it is likely the distilled water is at fault (at least partially).
  • Do not use a distillation system that contains metal parts (especially copper) as these can have biocidal effects. Low GGA results or BOD values can often be traced to this as a cause.
  • Try aging the distilled water in the incubator for up to one week (without nutrient buffers added). This will make sure that the water is saturated and will reduce the chance that the water will deplete more once it is used in the test.
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