Asbestos

What it is

Asbestos is a group of naturally occurring mineral fibers. In drinking water, it most often comes from the corrosion of older asbestos-cement water mains and from natural mineral deposits that the water passes through. The fibers are microscopic and do not change the taste, color, or smell of the water.

Why it matters

The EPA sets a federal maximum contaminant level (MCL) for asbestos of 7 million fibers per liter, counting fibers longer than 10 microns. That figure is the regulatory reference point for asbestos in public drinking water. We score whether a filter is certified to reduce this contaminant, not any health outcome.

What removes it

Asbestos is a mechanical fiber-reduction claim under NSF/ANSI 53, so a filter has to be tested and certified specifically for asbestos to earn credit for it, and reverse osmosis also reduces it. The trap is that a carbon filter is not automatically an asbestos filter: an ordinary carbon pitcher built for taste and chlorine does not carry the asbestos claim. Certification for asbestos by name is what separates a filter that reduces these fibers from one that simply improves taste.

Reference: EPA National Primary Drinking Water Regulations (asbestos MCL); NSF/ANSI 53 (asbestos fiber reduction).