How much salt a top-off adds in Austin

This guide from Sullivan's Pool Service summarizes the cited guidance. A tap water top-off adds only a small amount of salt. Austin Water's second quarter summary lists sodium at 28.5 mg/L, 18.6 mg/L and 26.4 mg/L, and chloride at 52 mg/L at Davis, 34 mg/L at Ullrich and 44 mg/L at Handcox, all far below the 250 mg/L chloride secondary standard recommended by TCEQ.

By Ryan Sullivan · Published October 16, 2026

Drafted with AI assistance from its cited sources and checked automatically before publication: every figure must appear in those sources. How our guidance is prepared.

What Austin tap water contains

Austin tap water carries sodium at modest levels, but the amount is not identical from one sample to the next. Reported figures for sodium in the finished water were 28.5 mg/L, 18.6 mg/L and 26.4 mg/L, so the concentration sits somewhere in the range between the low and high of those three measurements.

For a homeowner refilling a saltwater pool from the hose, that variation matters less as an exact number than as a pattern. Each gallon of top-off water brings some sodium with it, and the readings above show the supply does not deliver a fixed dose every time.

Even at these levels, the sodium arriving from the tap is small next to the salt already dissolved in a chlorinated pool, which is why the next section looks at how top-offs add up over repeated refills.

Why sodium matters when you top off

Sodium is one of the dissolved minerals that shows up in the local water supply, and it behaves differently from the other things a pool owner usually tracks. Unlike chlorine or pH, it does not react with anything in the water or fade over time. It simply stays put, so every top-off adds a little more on top of what is already there.

That matters because salt levels in a pool only move in one direction through ordinary filling. Evaporation leaves sodium behind, and replacement water brings a fresh supply with it. Splash-out and backwashing are the only routine ways it leaves the pool at all.

For someone deciding whether top-offs are quietly shifting their water chemistry, sodium is worth a look alongside the usual readings. The measurements discussed in the other sections are reported in milligrams per liter, which makes it possible to see how much of the mineral is arriving each time the water level gets topped up.

Chloride in the same finished water

Sodium gets most of the attention when pool owners think about tap water, but chloride is the other half of the salt picture. When water treatment plants report salt-related content, chloride readings show how much of the dissolved mineral load comes from that ion specifically, and Austin's treated water carries a modest amount of it.

At the Davis plant, chloride measured 52 mg/L. Ullrich came in lower at 34 mg/L, and Handcox fell between the two at 44 mg/L. All three readings sit well under the secondary standard of 250 mg/L, which is the benchmark used for aesthetic qualities in finished drinking water rather than a health-based limit.

For a pool owner, the practical takeaway is that topping off adds a small amount of chloride along with the sodium discussed elsewhere. The exact amount depends on which plant supplies the water at any given time, since the levels differ from one source to the next.

Where these numbers come from

Austin Water publishes quarterly summaries of what its plants produce, and the figures used in this section come from the second-quarter summary covering samples collected between April 1 and June 30. Those averages describe two different things, so it helps to keep them straight. Raw refers to untreated source water as it enters a plant, before any treatment. Tap refers to finished drinking water, sampled at the tap of the plant that produced it.

The city runs three treatment plants, Davis, Ullrich and Handcox, and the summary reports results for each. Because the numbers are averages over a sampling period rather than single readings, they give a reasonable picture of what was coming through the system during that stretch of spring and early summer.

When the later sections quote a figure, that number describes either the raw source water or the finished tap water, and the label matters. The difference between those two points is where treatment changes what ends up in the pool.

Standards behind the summary

Some numbers on a water quality report carry more weight than others. When a limit is written into the Safe Drinking Water Act as a maximum contaminant level, it is enforceable, meaning the utility is required to meet it. A secondary standard works differently. It is an aesthetic level, recommended rather than required, and the Texas Commission on Environmental Quality is the agency that recommends it for substances that affect taste, odor or appearance rather than health.

That distinction matters when reading the figures for sodium and chloride, since neither is usually governed by the same kind of enforceable ceiling as many other drinking water constituents.

For anyone who wants to check these figures directly, Austin Water publishes monthly and quarterly summaries of finished drinking water on its website, at austintexas.gov/water/water-quality-summaries. Those summaries are the public record behind the numbers discussed in the other sections here.

Next step: saltwater pool service.