Water Quality and Sampling
Water quality items test whether you can collect a sample that the laboratory will accept and interpret the result correctly for a homeowner.
Common parameters and benchmarks
- Total coliform with E. coli is the basic bacteriological test; any coliform detection requires investigation.
- Nitrate as nitrogen has a 10 mg/L maximum contaminant level; arsenic is 10 micrograms per liter.
- Iron, manganese, hardness, sulfate, and chloride explain staining, scale, and taste; PFAS and gross alpha are additional concerns in some areas.
Collection that passes laboratory review
- Use the laboratory's sterile 100 mL bottle for bacteria, do not rinse it, do not touch the rim, and leave the small headspace.
- Remove aerators and screens, run the water long enough to clear the service line, then fill.
- Chill the sample and deliver it within the holding time, generally 30 hours for bacteriological analysis.
- Sample raw well water, not softened or filtered water, when the question is what the aquifer contains.
Worked example
A nitrate result comes back at 12 mg/L as N. Reasoning: this exceeds the 10 mg/L MCL. The driller confirms the sample was taken before any softener, checks for septic or fertilizer sources nearby, and advises reverse osmosis or ion exchange at the tap, plus retesting. Boiling is specifically rejected because it concentrates nitrate.
Traps
- Sampling downstream of a softener or carbon filter.
- Rinsing the bacteriological bottle or filling it only partly.
- Recommending boiling for nitrate or bacteria without disinfection follow-up.
- Treating one clean sample as proof the well is sealed; construction defects often show up on resampling.