Drying sea salt at Maine Sea Salt Company in Marshfield, Maine.

Sodium is a naturally-occurring element that is found nearly everywhere in our environment, including being critical to animal biologic functioning, including our own. It is the seventh most common element on Earth.

Some sodium is found in all natural water supplies, but more so in areas where seawater may have intruded into a well or where road salt is used.  Home water softeners can also introduce salt into drinking water as a byproduct of removing dissolved minerals from hard water.

Sodium has no set hazardous exposure level, but those individuals on a low sodium diet should take into account the amount of sodium in their water when determining overall sodium intake. The US Secondary Drinking Water Standard for sodium has been set at 20 mg/L, being listed as a "nuisance" contaminant.

Exposure Limits

Maine Maximum Exposure Guideline limit: n/a

USA Primary Drinking Water Standard limit: n/a

USA Secondary Drinking Water Standard limit: 20 mg/L (Maine MEG); no EPA limit

Resources

State of New Hampshire "Sodium and Chloride in Drinking Water" (3 pg. pdf)

Wikipedia, "Sodium"

"The Mineralogy of Sodium," Mindata website: https://www.mindat.org/element/Sodium

US Centers for Disease Control, "Sodium"

MEL Test Methods for Sodium

Drinking Water – EPA 200.5 (SDWA Compliant)
Wastewater – EPA 200.7 R4.4 (NPDES Compliant)
Solids – EPA 6010B, 6010C (SW846) (RCRA Compliant)

Sample Requirements

Wastewater:

Container: plastic, glass
Volume: 250mL
Hold Time: 6 months if preserved with HNO3 to pH<2, otherwise 2 weeks
Preservation: HNO3 to pH<2

Solids:

Container: plastic, glass, baggie
Volume: a least 150g
Hold Time: 6 months
Preservation: n/a