Water filter guides

How filtration actually works, without the marketing. These pages explain the mechanisms so you can work out what your water needs, rather than buying a product and hoping.

• How do water filters work?

  The six mechanisms, from mechanical and carbon to ion exchange, reverse osmosis, UV and distillation. What each removes, what it misses, and why systems combine them.

• What a whole house filter costs

  The hardware is the smaller number. What each system costs to buy, what a year of cartridges costs, and the cost per thousand gallons that actually compares them.

• Installing a whole house water filter

  Where on the main line it belongs, why the bypass matters more than the filter itself, the housing order that ruins a cartridge, and the pressure you give up.

• Chlorine vs chloramine

  NSF certifies the two separately, and 5,553 models hold the chlorine claim against 216 for chloramine. Many utilities use chloramine, and it is the harder of the two to remove. Which one you have is in your annual water report.

• What is filtered water?

  The FDA defines artesian, mineral, purified, spring and well water, and mineral water has to carry 250 ppm of dissolved solids to use the name. "Filtered water" appears in that regulation once, in the list of terms it excludes.

• Do water filters remove microplastics?

  A size problem rather than a chemistry one, and there is a certification for it that almost nobody mentions. Microplastics reduction is one of sixteen separate claims under NSF/ANSI 401, so the badge on the box does not tell you whether a filter holds it.

• Does a Brita filter remove lead?

  The Elite is certified for 99.5% lead reduction and the standard filter is not certified for lead at all. Both are sold as certified, and neither certificate is held with the body most people search.

• Do water filters remove fluoride?

  Carbon filters remove almost none. Reverse osmosis removes 85–95%, and three other methods work. The full comparison, plus how to check a certificate.

Looking for a recommendation instead? We score and rank under-sink reverse osmosis systems for drinking water and whole house systems for treating the whole property, and how we rate publishes the formula behind every score.