Most people who look into reverse osmosis in San Antonio already know the water is hard. What they want to know is whether the water they drink needs anything more.
Below: what is in SAWS water, what reverse osmosis takes out of it, and why it is the step you add at the kitchen sink on top of a softener. The figures come from the San Antonio Water System's own reports.
What is in San Antonio tap water?
SAWS water is mostly groundwater. Its 2026 Water Quality Report, covering 2025 testing, lists the Edwards, Carrizo, Simsboro, Trinity and Wilcox aquifers, plus surface water from Canyon Lake in some areas.
Water that moves through rock picks up what the rock is made of. In San Antonio, that is mostly calcium and magnesium, which is why SAWS gives typical hardness as 15 to 20 grains per gallon. What that does to a house is covered in our article on San Antonio hard water.
The same report covers the rest:
- No violations. SAWS reports that its system received no violations in 2025.
- Chlorine. SAWS adds chlorine to keep bacteria out of the pipes on the way to you. The report puts the average free chlorine in the system at 1.46 parts per million, with readings from 0.16 to 3.7.
- Nitrate. The highest level SAWS measured at its plants was 2.45 parts per million. The federal limit is 10.
- Lead. In the 2024 round of tap sampling, the 90th percentile result was 1.6 parts per billion, against an action level of 15, and no site went over.
On lead, SAWS is direct about where it comes from: mostly the service line and the plumbing inside the home, which the utility does not control. Lead service lines were banned in 1989, and SAWS is offering a service line inspection to homes built before then whose line material is still unknown.
What the report does not show
Minerals such as calcium, sodium and iron are what SAWS calls secondary constituents. They affect taste, color and odor, not health, and the state regulates them, so the report leaves them out and points to the Texas Drinking Water Watch database.
Is San Antonio tap water safe to drink?
By the report, it meets federal standards, and we are not going to tell you otherwise. SAWS also says that when water meets federal standards, there may not be any health benefit to buying bottled water or a filter at the tap.
So why put reverse osmosis in? The reasons are practical ones: the chlorine taste, plumbing in an older house that you cannot see inside, and wanting one tap you never have to think about for drinking, cooking, coffee and ice.
Not sure what your home needs at the kitchen sink?
Tell us where you live and what you are noticing in the water you drink. We will tell you which system fits and what it costs.
Why reverse osmosis is the drinking water step
A softener and a reverse osmosis system do two different jobs.
A softener treats every drop that comes into the house. It takes out the calcium and magnesium that build scale in your water heater, fixtures and appliances.
Reverse osmosis, or RO, pushes water through a membrane fine enough to hold back what a whole-home system is not designed to catch: dissolved solids, chlorine and heavy metals such as lead. It sits under the kitchen sink and feeds its own faucet.
That is why the two go together. The softener protects the house. The RO handles the glass of water.
The RO systems we install in San Antonio
We carry two RO systems and an add-on that pairs with either. All three are below.
HW800 AlkaPro tankless RO
The HW800 AlkaPro is a tankless system, so there is no storage tank taking up your cabinet. It is rated at 800 gallons per day, with 7 stages of filtration down to 0.0001 micron, and it is certified to NSF/ANSI 58, the standard for reverse osmosis drinking water systems.
It is rated to remove lead and other heavy metals, dissolved solids and chlorine, and it finishes with a coconut-shell carbon block for taste. The filters use quick-connect fittings, so you can change them yourself.
5-Stage Tank RO
The 5-Stage Tank Reverse Osmosis system is the traditional design: five stages, a 100 gallon per day membrane and a pressurized storage tank, with its own drinking water faucet. It removes dissolved solids, chlorine and heavy metals. Replacement filters are easy to find, and installation is free.
Pure Alkaline Filter
RO is thorough. It takes out the good minerals along with everything else, and some people miss that taste. The Pure Alkaline Filter installs inline with either RO system and adds calcium and magnesium back in, so the water tastes more like spring water. It is a simple cartridge to replace.
Choosing between tankless and tank RO?
Call or fill out the form. Tell us how many people live in the house and we will tell you which one fits and what it costs.
Which one fits your home?
Go tankless with the HW800 if you want water on demand and your cabinet back. Go with the tank system if you want the proven design at a lower price. Add the alkaline filter to either one if taste is why you are buying.
No softener yet? Ask about both at once. They cover the two separate problems San Antonio water brings. Our San Antonio service area page covers how we work in the city.
Reverse osmosis in San Antonio: common questions
Does reverse osmosis remove hardness?
At the kitchen sink, yes. The calcium and magnesium that make water hard are dissolved minerals, and RO takes dissolved solids out. It only treats that one faucet, though, so it does nothing for your water heater. That is a softener's job.
Do I need RO if I already have a softener?
A softener is built to stop scale, not to take dissolved solids and heavy metals out of the water you drink. If drinking water is the concern, RO is the step that handles it.
Talk to us about the right drinking water system for your home.
Call or fill out the form for system details and a price. We serve homes across San Antonio and the surrounding area.