“Water purification” is a word that sells. On its own it does not tell you what a system removes, how well, or whether anyone has checked. In San Antonio, where SAWS water runs a typical 15 to 20 grains of hardness, a “purifier” might be a reverse osmosis unit, a carbon filter, or something else entirely. This article explains what each method does, in the words of the EPA and the standards that certify them.
Start with what you want to remove
The Texas Commission on Environmental Quality’s guide to home water treatment asks one question first: “What contaminant do you want to remove or reduce?” It then advises choosing a unit certified by NSF, Underwriter’s Laboratory or the Water Quality Association to remove that contaminant, and making sure the unit is certified for it. That is the test for any “purifier”: certified, for what?
Reverse osmosis
Reverse osmosis is one method sold as purification for drinking water. The EPA describes it as “the process by which pressure forces water through a semi-permeable membrane.” A point-of-use system is connected to a single fixture, such as under the kitchen sink. The EPA says RO systems “can potentially remove water contaminants such as lead, volatile organic compounds (VOCs), PFAS, arsenic, bacteria, and viruses.”
Two points to weigh. First, reject water: the EPA says a typical point-of-use unit sends five gallons or more down the drain for every gallon of treated water, and some up to 10, while units with the WaterSense label must send 2.3 gallons or less. Second, the license: in Texas, work on RO equipment needs a Class III Water Treatment Specialist, or supervision by one, unless the person is a licensed plumber. The standard to ask about is NSF/ANSI 58. More on the reverse osmosis page.
Carbon and drinking water filters
Filters are certified to different standards for different jobs. NSF/ANSI 42 covers aesthetic effects such as chlorine, taste and odor. NSF/ANSI 53 covers health effects such as lead. NSF/ANSI 401 covers incidental contaminants. A filter can be whole-house or at one tap; see whole-house filters. A filter certified for taste and odor is not, for that reason, certified for lead, so read the listing.
Ultraviolet
Ultraviolet (UV) systems have their own standard, NSF/ANSI 55, with a Class A and a Class B. If UV is suggested, for example for a private well, a laboratory test should come first. Ask what class a UV unit is certified to and what it is meant to treat in your water.
What purification does not include: hardness
Removing hardness is softening, not purification. SAWS says hard water is not a health hazard; hardness is about scale, spots and soap. A softener certified to NSF/ANSI 44 deals with it. Homes that want both soft water and RO drinking water need both pieces of equipment. See water softeners in San Antonio.
PFAS and purification claims
PFAS is one reason people ask about purification. The EPA’s final rule set limits of 4.0 parts per trillion for PFOA and for PFOS in public water. On May 18, 2026 the EPA proposed keeping those limits with two more years, to 2031, for water systems to comply, and rescinding the limits for PFHxS, PFNA, HFPO-DA (GenX) and the hazard index. As of October 2026 those were proposals, not final rules. For what your utility found, read its annual report. For equipment, ask for certification to reduce PFAS specifically.
The permit: “water purifier”
The City of San Antonio’s own bulletin uses the word. Information Bulletin 121c says the Limited Service Repair permit program covers the like-for-like replacement of an existing water purifier or water softener, and installing one in an existing building that is already pre-plumbed. Other work needs a regular plumbing permit. Ask the installer which applies.
Questions for any purifier quote
- Which contaminants is this unit certified to reduce, and under which NSF/ANSI standard?
- What did your test of my water show?
- How much water does it send to the drain?
- Which Texas license do you hold for this equipment?
- Which San Antonio permit applies?
- What upkeep does the maker specify?
Questions people ask
What is the best water purification system?
The one certified to reduce what you want removed from your water. Decide that first, from a report or test, then compare units by NSF/ANSI standard.
Does a purifier make my water healthier?
This site makes no health claims. For health questions about your water, ask your doctor, and read your utility’s annual water quality report.
Is a water purifier the same as a water softener?
No. A softener removes hardness under NSF/ANSI 44. A purifier is a sales word for equipment such as reverse osmosis or filters, each certified to its own standard for specific contaminants. San Antonio’s LSR permit bulletin names both.