On this page, reverse osmosis in San Antonio means a compact system under the kitchen sink that makes drinking and cooking water at its own small faucet. This page explains how RO works, the water it sends down the drain, the standard and the Texas license that apply, and how RO fits with a softener on SAWS water.
Water Filtration San Antonio is an independent referral service, not an installer or plumber. When you send the form, your details go to an independent local water treatment pro who can contact you and quote the work.
How reverse osmosis works
The EPA defines reverse osmosis as “the process by which pressure forces water through a semi-permeable membrane.” Water that passes through is the treated water, called permeate. Water that does not carries away what the membrane held back, and goes to the drain as reject water, called concentrate or brine. A point-of-use system, in the EPA’s words, is “connected to a single fixture (e.g., under the kitchen sink).”
According to the EPA, RO systems “can potentially remove water contaminants such as lead, volatile organic compounds (VOCs), PFAS, arsenic, bacteria, and viruses.” What a particular unit is certified to reduce is on its listing, so ask for it.
The water RO sends down the drain
RO uses water to make water. The EPA says a typical point-of-use RO system will generate five gallons or more of reject water for every gallon of treated water, and some inefficient units up to 10. Systems with the EPA’s WaterSense label must send 2.3 gallons or less down the drain per gallon treated. That difference is worth asking about.
| Unit | Reject water per gallon treated (EPA) |
|---|---|
| Typical point-of-use RO | 5 gallons or more |
| Some inefficient units | Up to 10 gallons |
| WaterSense labeled RO | 2.3 gallons or less |
RO and a softener on SAWS water
A softener and an RO unit do different jobs. With SAWS water at a typical 15 to 20 grains per gallon, the softener handles hardness for the whole house. The RO unit at the kitchen sink makes drinking and cooking water. Ask the installer whether the RO unit would be fed from softened or hard water in your house, and why.
Want RO drinking water at the kitchen sink? Ask an independent San Antonio pro for a quote.
Request a quoteThe standard and the Texas license
NSF/ANSI 58 is the standard for reverse osmosis drinking water treatment systems. TCEQ advises choosing a unit certified by NSF, Underwriter’s Laboratory or the Water Quality Association to remove the contaminant you are concerned about. Ask which contaminants your unit’s certification covers.
Texas sets a higher bar for RO work than for softeners. Under TCEQ’s Water Treatment Specialist rule, work on reverse osmosis and deionization equipment needs a Class III license, or supervision by a Class III holder. Plumbers licensed under Texas Occupations Code Chapter 1301 are exempt from the Water Treatment Specialist license. Ask which one the installer holds.
Upkeep of an RO unit
An RO system has filters and a membrane that wear out in use, and each has its own replacement schedule from the maker, so keep the manual and the part numbers. Ask the installer to label the housings, to show you how to shut off the unit’s water supply, and to tell you what a service visit would include. If the unit starts sending water to the drain all the time, or the small faucet slows to a trickle, ask for it to be checked.
Because servicing RO equipment in Texas needs a Class III Water Treatment Specialist, or supervision by one, unless the person is a licensed plumber, ask the same license question at a service visit that you asked at the install.
Whole-house reverse osmosis
RO for the whole house is a different project from an under-sink unit. A whole-house RO system is a bigger installation, and the installer sizes it after a water test. If you are quoted one, ask why under-sink RO plus a softener would not do the job, how much reject water the system sends to drain, and what its upkeep involves.
Questions to ask before you buy
- Which contaminants is this unit certified to reduce under NSF/ANSI 58?
- Does it carry the EPA WaterSense label, and how much reject water does it make?
- Where will the drain connection and the storage tank go?
- Will it be fed from softened water or hard water?
- Which Texas license do you hold for RO work?
- What does the maker say about replacing the filters and the membrane?
For other kinds of water treatment, see water treatment in San Antonio. For servicing an RO unit you already have, see softener and filter service.
Questions people ask
What is the downside of reverse osmosis?
Reject water. The EPA says a typical point-of-use unit sends five gallons or more to the drain per gallon treated. WaterSense labeled units must send 2.3 gallons or less.
Is RO water hard on the kidneys?
This site does not give medical advice. If you have a health question about your drinking water, ask your doctor.
How much does reverse osmosis cost in San Antonio?
This site prints no prices. Ask for a written quote naming the unit, its NSF/ANSI 58 certification and the installation work.
Who can install an RO system in Texas?
Under TCEQ’s rule, RO work needs a Class III Water Treatment Specialist or supervision by one. Texas licensed plumbers are exempt from that license.
Can I put RO on the whole house instead?
A whole-house RO system is a bigger installation, and the installer sizes it after a water test. Ask why an under-sink unit plus a softener would not do the job, and how much reject water the whole-house system would send to the drain.
Does an RO unit soften water?
An under-sink unit treats the water at one faucet only. Hardness for the whole house is a softener’s job, under NSF/ANSI 44. With SAWS water at 15 to 20 grains, homes that want both soft water and RO drinking water need both.
