What is the best water source to use for sample preparation and dilution following the BOD method?

Document ID

Document ID TE178

Version

Version 5.0

Status

Status Published

Published Date

Published Date 08/20/2019
Question
What is the best water source to use for sample preparation and dilution following the BOD method?
Summary
Sources of dilution water for the BOD method
Answer
Quality dilution water is very important when testing Biochemical Oxygen Demand (BOD), as any contamination in the water will cause problems with the test.

Distilled and Deionized Water are commonly used in BOD testing. However, the most practical way to consistently produce water of low organic content is by distillation with alkaline permanganate. Commercial stills can be set up to produce high quality distilled water automatically. When a still is fed with chlorinated water, some chlorine may distill over with the water. if this occurs, the chlorine must be destroyed using thiosulfate.

It is not recommended to use deionized water from an ion exchange column. Experience has shown that deionized water, particularly from a new demineralizer with new resin, often contains substantial amounts of organic matter, that is released intermittently and is undetectable with a conductivity  water purity gauge. Also, the large surface-to-volume ratio that exists in the columns because of the resin beads encourages bacterial growth in the column.

 

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