Short answer: treatment decisions rest on a few numbers: hardness (gpg or mg/L), chlorine or chloramine residual (mg/L), pH, TDS (mg/L) and iron (mg/L). Health decisions rest on laboratory results compared with regulatory limits (MCLs). An in-home screening gives you the first set; only a certified lab gives you the second. TDS, in particular, tells you how much is dissolved, not whether any of it is harmful.
Units you will see
- mg/L (milligrams per liter) and ppm (parts per million) are, for water, the same thing.
- µg/L (micrograms per liter) or ppb (parts per billion): one thousandth of a mg/L. Lead, arsenic and PFAS limits are usually in these units. (PFAS limits are often in ng/L, parts per trillion.)
- gpg (grains per gallon): the traditional hardness unit in the treatment industry. 1 gpg = 17.1 mg/L as calcium carbonate.
- NTU: turbidity, a measure of cloudiness.
- pH: acidity on a 0–14 scale; 7 is neutral. EPA's secondary guideline for drinking water is 6.5–8.5.
- CFU/100 mL or present/absent: bacteria results. Total coliform should be absent.
Treatment-related measurements
| Measurement | What it tells you | Typical use in a recommendation |
|---|---|---|
| Hardness | Calcium and magnesium as CaCO₃. WQA classes: 0–1 gpg soft; 1–3.5 slightly hard; 3.5–7 moderately hard; 7–10.5 hard; above 10.5 very hard | Whether to soften; resin capacity sizing |
| Chlorine / chloramine residual | Disinfectant remaining at your tap, mg/L. EPA maximum residual is 4 mg/L; typical residential levels 0.5–1 mg/L | Whether filtration media is needed and expected media life |
| pH | Below ~6.5 is corrosive to copper and lead plumbing; above ~8.5 can scale and taste bitter | Flags corrosion; may call for neutralization ahead of other treatment |
| TDS | Total dissolved solids, mg/L: all dissolved minerals and salts combined | Baseline for RO performance (RO typically reduces TDS substantially). Not a safety measure |
| Iron / manganese | Dissolved metals that stain; EPA secondary guidelines 0.3 and 0.05 mg/L | Oxidation/filtration before softening; softener iron allowance |
| Turbidity / sediment | Particles in suspension | Mechanical filtration ahead of other equipment |
TDS is not a safety assessment
Low TDS does not mean safe, and high TDS does not mean unsafe. Spring water prized for taste can read 300 mg/L; distilled water reads near zero and contains nothing good or bad. TDS is useful for checking that a reverse-osmosis system is working (treated water should be a small fraction of the feed) and for nothing else. Any sales pitch built on a TDS meter alone is incomplete.
Health-related measurements (laboratory only)
These are compared against Maximum Contaminant Levels (MCLs) set by EPA and New York State. The lab report lists the result, the limit, and the method. Common ones for our region:
- Total coliform and E. coli: should be absent. A positive means disinfection or well repair, not a softener.
- Nitrate: MCL 10 mg/L as nitrogen. A concern near farmland and septic systems, and for infants.
- Lead and copper: federal lead action level 15 µg/L, scheduled to drop to 10 µg/L under EPA’s 2024 rule revisions. Usually from household plumbing; a first-draw sample is needed.
- Arsenic: MCL 10 µg/L; naturally occurring in some bedrock in New York.
- PFOA / PFOS: New York State set 10 ng/L MCLs for each in 2020; EPA finalized federal limits of 4 ng/L in 2024. Limits and their compliance timelines are subject to regulatory change; check the current value with your lab.
- VOCs, radon, uranium: tested when local geology or history suggests them.
For each of these, the question "is there treatment?" has a certified answer for specific equipment. The Micromax 8500, for example, is certified under NSF/ANSI 58 to reduce lead, arsenic, fluoride and others, and under 53 to reduce PFOA/PFOS. A certification does not mean the contaminant is in your water; the lab result establishes that.
Screening versus accredited laboratory results
| In-home screening (treatment dealer) | ELAP-certified laboratory | |
|---|---|---|
| Method | Field test strips, titration, meters | Accredited methods with quality control and chain of custody |
| Good for | Hardness, chlorine, TDS, pH, iron; equipment selection | Compliance-grade results for health decisions |
| Not good for | Bacteria, metals at µg/L, PFAS, VOCs | Nothing; cost and turnaround are the trade-off |
| NYS guidance | Do not rely on vendor tests for health decisions | Required for private-well health testing |
Using your results in a treatment conversation
- Sort the findings into "nuisance" and "health." Hardness, chlorine, iron staining and taste are nuisance. Anything over an MCL is health, and the health findings set the order of work.
- Ask what each proposed piece of equipment is certified to do and which finding it responds to. If a proposal does not map to a finding, ask why it is there.
- Ask what will be re-tested after installation and how you will know the system is working (hardness at a tap, TDS before and after an RO, a follow-up lab test for a health contaminant).
- Keep the reports. A baseline makes future changes obvious and is useful if you sell the house.
Bring your results to the in-home assessment or send them with your request. We read them with you, line by line, and we will tell you which findings do not need treatment at all.