NSF 42 vs 53 vs 401 vs 44 vs 55 vs 58

Quick answer: The standard number tells you what type of performance or technology is being evaluated; it is not a 1-to-100 quality score.

NSF/ANSI water treatment standards is easier to answer when you separate marketing language from the actual hydraulic, treatment and ownership requirements of your house. FilterTier uses the same framework across products so you can compare systems without learning every brand's terminology first.

NSF/ANSI 42

Commonly covers aesthetic effects such as chlorine, taste and odor reduction. A 42 claim can be valuable, but it does not by itself prove a health-effect contaminant reduction.

NSF/ANSI 53

Covers specified health-effect contaminant reduction claims. Always check which contaminant the exact model is certified to reduce; 53 does not mean a system removes every contaminant covered anywhere in the standard.

NSF/ANSI 401

Covers specified emerging or incidental compounds. Again, the exact compound list matters.

NSF/ANSI 44, 55 and 58

Standard 44 applies to residential cation-exchange softeners, 55 to ultraviolet treatment systems, and 58 to reverse osmosis systems. These describe different technologies and performance requirements.

How FilterTier uses this information

The Find My Filter tool combines this factor with your water source, contaminants, peak flow, maintenance tolerance, warranty preference, manufacturing preference and budget. The product may still be excellent overall and a poor fit for your specific house — that is why WaterScore and Your Fit are separate.

You can also browse all systems, review our scoring methodology, or see how we handle maintenance and warranty.

Primary references

• NSF standards for water treatment systems