Frequent Questions

Most Drinking Water containers for bacterial collection has Na Thio calculated for 100ml. Can a laboratory invalidate a sample if it arrives with 110ml? Is there a EPA reference?

Most manufacturers include enough Sodium Thiosulfate in the bottles enough to neutralize more chlorine than would be present in drinking water (for instance, IDEXX includes enough to neutralize 50 mg/L chlorine) – as often the bottles are also used for wastewater, which is likely to have a much higher chlorine residual than drinking water.

So, while one could contact the manufacturer to be certain –most sample bottles contain more than enough sodium thiosulfate to neutralize any chlorine residual that may be present in the water sample, even if the volume of the water sample exceeds 100 mL.  Another alternative is to could check the chlorine residual of the remaining water sample in the sample bottle (after removing the 100 mL portion needed for the drinking water analysis so as not to risk contamination of the sample), to ensure all chlorine has been neutralized. There are test strips sold for this type of testing.
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