Filling a Pool in Arlington: Your Tap Water’s Starting Numbers
Filling a pool in Arlington means starting from Arlington Water Utilities (City of Arlington)’s water — which is moderately hard at roughly 94 mg/L total hardness (about 5.5 grains per gallon). Here is what those published numbers actually do to a pool — and what they do not.
Which way this water pushes a pool
At a typical 84 F pool temperature the published Arlington Water Utilities (City of Arlington) numbers index at +0.20 — inside the balanced band (how this is calculated). That puts Arlington 12th of the 15 cities here that publish enough to compute an index, counting from the most scale-forming down.
Since utilities publish TOTAL hardness and the index wants the CALCIUM fraction, +0.20 is a ceiling and the true figure sits at or below it — which for a near-balanced reading means Arlington water can test slightly aggressive once it is in the pool. Worth knowing before you assume balanced water needs nothing.
The top-off arithmetic
Evaporation removes pure water and leaves the minerals behind, so make-up water re-adds Arlington hardness every time. Replacing one full pool volume through top-off adds roughly another 94 ppm; starting from a fresh fill at about 94 mg/L, that reaches the 400 ppm ceiling after about 3.3 pool volumes of make-up water — a comfortable margin you are unlikely to burn through quickly. That is the 24th shortest budget of the 27 cities in this lookup.
Evaporation-only and deliberately the fastest case: splash-out, backwash and rain all dilute, and this uses published total hardness rather than the calcium fraction a kit reads (how this is calculated).
How much your own tap may differ
Less than you might think. Arlington Water Utilities (City of Arlington) publishes a tight range — 80 to 110 mg/L, only 1.4x end to end — which is unusual on this list and genuinely useful: it means the figures above are stable enough to plan around rather than merely a system-wide average hiding a lot of variation.
Why Arlington water is like this
VERIFIED IN THE MAIN. Arlington’s fill water is not local Tarrant County runoff, and that is the whole story. Lake Arlington sits inside the city limits, so it is natural to assume the tap is local lake water – but TRWD’s plan states the Tarrant County lakes (Arlington and Benbrook) function as TERMINAL STORAGE for the regional system. Water from the East Texas reservoirs is delivered into that terminal storage.
So Arlington’s mineral content tracks the TRWD regional blend – Cedar Creek and Richland-Chambers water piped up from roughly 75 to 90 miles southeast – rather than the geology of the ground the lake sits on. Second reason the numbers land where they do: neither plant softens. Both are conventional surface water plants – coagulation with aluminum sulfate plus a cationic polymer to floc and settle solids, then filtration and chloramine disinfection.
With no lime softening in the train, tap hardness is essentially the blended reservoir hardness passed straight through, which is why Arlington sits in the same moderate band as Fort Worth (both are TRWD customers drinking largely the same regional water) rather than in the high band of limestone-aquifer Texas cities.
CAUTION FOR PUBLICATION: the Fort Worth Report article that documents the treatment process also carries a hardness comparison (Arlington 5 grains per gallon vs Austin 11, Houston 8, San Antonio 21) sourced to HydroFLOW USA, a water-treatment vendor. That comparison is vendor data, not utility data, and should not be published as authoritative. I could not extract Arlington’s own 2025 Water Quality Report because the city publishes it only as a Joomag flipbook.
Conventional surface water treatment at both plants: aluminum sulfate plus a cationic polymer as coagulant to clump and settle solids, then filtration, with chloramine (chlorine plus ammonia) disinfection. No lime softening identified. Pierce-Burch, 17 years older than Kubala, is in the middle of a $112.5 million improvement project including new chemical treatment facilities.
Arlington’s own laboratory tests pH and hardness on samples from reservoirs, treatment plants and distribution sites – 7,305 samples analyzed in 2023, screening for about 370 substances – and also runs the water quality testing for smaller TRWD-supplied cities such as Kennedale, Mansfield and Waxahachie.
VERIFIED AND STRONG, straight out of the City of Arlington’s own engineering document, and it lands exactly on pool season. Arlington’s RFQ WUTR16011 for the Lake Arlington Raw Water Pump Station states: ‘Since its construction, the LARWPS has been the primary supply of raw water to the Pierce-Burch (PB) Water Treatment Plant (WTP) which is rated to treat 75 MGD,’ and then: ‘The pump station operates for about 8 months of the year.
PB WTP is shut down during most of the winter due to the lower demand when the John F. Kubala WTP supplies the total demand of the City.’ So Arlington runs on ONE plant in winter and TWO in the warm months. In winter, 100 percent of the city’s water comes through Kubala. From roughly spring through fall – precisely when pools are being filled and topped off – Pierce-Burch also comes online drawing Lake Arlington raw water through the LARWPS.
Which plant’s water reaches a given address, and therefore its exact chemistry, changes with the season. The demand swing is large: about 100 million gallons a day citywide in summer versus about 40 million in winter. NOT VERIFIED: several secondary sources state that Kubala takes East Texas reservoir water directly from a TRWD pipeline.
That is plausible and consistent with the terminal-storage arrangement, but I did not open a primary source confirming Kubala’s specific raw-water feed, so it should not be published as fact.
Background sources: arlingtontx.gov, wbcsouthwest.org, trwd.com, fortworthreport.org.
Worth a look next door
- Filling a pool in San Antonio — Same state, different water: San Antonio fills at about 300 mg/L against 94 here.
- Filling a pool in Glendale — The other end of the scale: Glendale gets about 0.7 pool volumes of top-off against 3.3 pool volumes here.
Source: City of Arlington 2025 Water Quality Report (official flipbook: viewer.joomag.com/2025-water-quality-report-water-quality-report/0340722001778252923); 2023 WQR: viewer.joomag.com/2023-water-quality-report-2023-water-quality-report/0661026001714671539 (2025 report data), accessed 2026-08-11. Values are the utility’s published system-wide figures; your tap can vary by service zone and season.
Data page generated 2026-08-15. Part of the pool fill-water lookup.