WaterAnswer.com

The most useful “tool” for most water quality questions is a good guide. Before buying a filter or a test kit, knowing exactly what you’re dealing with saves time and money.

External Resources Worth Bookmarking

These are the best free data sources for water quality research:

EWG Tap Water Database — ewg.org/tapwater Search your ZIP code or utility name to see what contaminants have been detected in your city water. Shows both EPA legal limits and EWG health-based guidelines (which are more conservative). Free.

MyTapWater.org — mytapwater.org Cleaner interface than EWG for a quick lookup. Shows contaminant levels and how they compare to EPA standards. Good starting point for city water.

EPA Private Wells — epa.gov/privatewells The EPA’s resource hub for private well owners. Includes a certified lab locator, contaminant fact sheets, and well maintenance guides. The most authoritative source for well owners who have no utility to call.

NSF Certified Product Listings — info.nsf.org/Certified/DWTU/ Search for any water filter by brand or model to verify its NSF certification and what contaminants it’s actually certified to reduce. Don’t trust “tested to NSF standards” claims — look up the certification directly.

Water Quality Association — wqa.org Industry trade group with consumer resources on hardness, treatment technologies, and finding certified water treatment professionals.

Quick Reference: Water Hardness Scale

Grains per Gallon (gpg) mg/L as CaCO3 Classification
0–1 0–17 Soft
1–3.5 17–60 Slightly hard
3.5–7 60–120 Moderately hard
7–10 120–180 Hard
10+ 180+ Very hard

To convert: divide mg/L by 17.1 to get gpg.

Quick Reference: NSF Standards

Standard What It Covers
NSF 42 Chlorine taste/odor, aesthetic issues
NSF 53 Lead, cysts, VOCs, health-effect contaminants
NSF 58 Reverse osmosis (PFAS, arsenic, nitrates, fluoride)
NSF 401 Emerging contaminants (pharmaceuticals, pesticides)
NSF 55 Class A UV disinfection — purification level
NSF 55 Class B UV disinfection — supplemental only
NSF 177 Shower filtration

A filter certified under NSF 53 is not automatically certified under NSF 58. Always check the specific certification for the contaminant you’re targeting.

Guides That Replace a Calculator

What Water Filter Do I Need?

Match your contaminant to the right NSF standard and filter type. The decision guide that most sites skip.

How to Test Well Water

What to test for, how often, how to find a certified lab, and how to read the results.

How to Read Your Water Quality Report

Your utility sends a CCR every year. Here's what the numbers actually mean.

Frequently Asked Questions

How do I look up what's in my city tap water?
The EWG Tap Water Database (ewg.org/tapwater) lets you search by ZIP code or utility name. It shows detected contaminants alongside both EPA legal limits and EWG health-based guidelines. MyTapWater.org is another option. For private wells, no equivalent database exists — you need to test your own water.
How do I convert water hardness from mg/L to grains per gallon?
Divide mg/L (as CaCO3) by 17.1 to get grains per gallon (gpg). For example, 171 mg/L equals 10 gpg. Your utility's Consumer Confidence Report usually lists hardness in mg/L. Water softener sizing is typically done in gpg.
Where can I find a certified lab to test my water?
The EPA maintains a list of state-certified drinking water labs at epa.gov/privatewells. Your state health department also maintains a list. For well water, your state's cooperative extension service often offers low-cost or subsidized testing.