Filling a Pool in Fort Worth: Your Tap Water’s Starting Numbers
Filling a pool in Fort Worth means starting from Fort Worth Water (City of Fort Worth Water Department)’s water — which is hard at roughly 129 mg/L total hardness (about 7.5 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 Fort Worth Water (City of Fort Worth Water Department) numbers index at +0.51 — mildly scale-forming (how this is calculated). That puts Fort Worth 6th of the 15 cities here that publish enough to compute an index, counting from the most scale-forming down.
Read it as a ceiling rather than a verdict: utilities publish TOTAL hardness while the index wants the CALCIUM fraction, so the true figure sits at or below +0.51 — close enough to the balanced band that it should not alarm you. What it does settle is which mistake costs money in Fort Worth. Cloudy water and scale at the tile line are the failure mode here; etched plaster is not.
The top-off arithmetic
Evaporation removes pure water and leaves the minerals behind, so make-up water re-adds Fort Worth hardness every time. Replacing one full pool volume through top-off adds roughly another 129 ppm; starting from a fresh fill at about 129 mg/L, that reaches the 400 ppm ceiling after about 2.1 pool volumes of make-up water — a couple of pool volumes, which a high-evaporation summer gets through faster than most owners expect. That is the 21st 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. Fort Worth Water (City of Fort Worth Water Department) publishes a tight range — 108 to 150 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 Fort Worth water is like this
VERIFIED. Fort Worth’s fill water is a blend of two hydrologically different supplies, and that is exactly why the published figures are RANGES rather than single numbers.
Supply one is the local West Fork Trinity system – Lake Bridgeport, Eagle Mountain Lake, Lake Worth, Benbrook Lake and the Clear Fork – sitting in a drier zone where, in the utility’s own words, ‘the average annual rainfall totals about 37 inches.’ Supply two is East Texas: Cedar Creek and Richland-Chambers reservoirs, roughly 75 and 90 miles southeast, in a wetter zone with ‘just over 40 inches a year,’ piped 250 miles into Tarrant County.
Different watersheds, different runoff chemistry, blended in proportions that change. The 2023 report’s own ranges show the spread: Total Hardness as CaCO3 79.9 to 134 ppm (5 to 8 grains per gallon), Total Alkalinity as CaCO3 88.3 to 141 ppm, Total Dissolved Solids 184 to 274 ppm, Sulfate 28.4 to 48.0 ppm. That is roughly a 68 percent spread in hardness across the system.
IMPORTANT CORRECTION FOR PUBLICATION: filter-vendor pages widely claim Fort Worth is ‘hard to extremely hard’ and ‘ranks #6 in the nation for water hardness.’ The utility’s own published range tops out at 134 mg/L, which is only moderately hard. Do not repeat the vendor claim. Treatment is chloramination (2023 chloramine average 3.4 ppm, range 0.72 to 4.4 ppm); no lime softening appears in the report, so the tap hardness is essentially the blended raw-water hardness rather than a treatment-set value.
Chloramines used as the disinfectant residual (2023 average 3.4 ppm, range 0.72 to 4.4 ppm). Conventional surface water treatment; no lime softening found in the 2023 report. PFAS note with a geographic angle: the report states results above the future EPA limits at the North Holly and South Holly plants, ‘facilities [that] treat water originating primarily from Lake Worth,’ and Fort Worth has been working since December 2023 on adding PFAS treatment at those two plants.
TCEQ classified the risk to Fort Worth’s source waters as high for most contaminants (a susceptibility rating, not a statement that health risks are present).
VERIFIED AND MECHANISTIC. Two independent drivers. (1) SOURCE SWITCHING BY RESERVOIR LEVEL: TRWD’s 2024 plan states ‘The TRWD system operation plan calls for a shift in water supply deliveries from the East Texas reservoirs if the combined storage capacity in Lake Bridgeport and Eagle Mountain Lake falls below 50 percent.’ So when the local West Fork lakes draw down, the blend swings toward Cedar Creek and Richland-Chambers water – a different watershed with different mineral content.
Fill-water chemistry therefore tracks drought and reservoir storage, not the calendar alone. (2) PLANT-BY-PLANT DIFFERENCES: Fort Worth runs multiple plants on different intakes – North Holly and South Holly treat water ‘originating primarily from Lake Worth,’ while Rolling Hills has treated Cedar Creek water since 1972.
TRWD even operates to ‘maintain the elevation of Lake Worth to support the intake of Fort Worth’s Holly Water Treatment Plant.’ Which plant serves an address determines where in the 79.9-134 ppm hardness band that address actually falls. A pool owner testing their own fill water is doing something genuinely more accurate than reading a citywide average.
Background sources: fortworthtexas.gov, codelibrary.amlegal.com, trwd.com, waterdatafortexas.org.
Before you drain or refill in Fort Worth
A) DROUGHT (2024 Drought Contingency and Emergency Water Management Plan). The plan’s definition of ‘Non-essential water use’ includes ‘Filling, refilling, or adding to any swimming pools or Jacuzzi-type pools, except to maintain safe operating levels,’ and Stage 1 directs the city to ‘Initiate mandatory restrictions to prohibit non-essential water use.’ STAGE 1 (Water Watch, 5 percent reduction goal; triggers include TRWD combined reservoir storage dropping below 75 percent of conservation storage capacity): ‘Discourage the filling, draining, or refilling of swimming pools, wading pools, hot tubs and Jacuzzi type pools except to maintain adequate water levels for structural integrity, proper operation and maintenance, and/or to alleviate an issue that poses a public safety risk.’ STAGE 2 (Water Warning): same discouragement, plus ‘Encourage the use of covers for all types of pools, hot tubs, and Jacuzzi type pools when not in use,’ plus discouraging ornamental fountains/ponds on potable water unless they support aquatic life or have a recirculation system. STAGE 3 (Emergency Water Use) is the hard stage, verbatim: ‘Prohibit the draining, filling, or refilling of swimming pools, wading pools, hot tubs, and Jacuzzi type pools. Existing private and public pools may add water to maintain pool levels; however they may not be refilled using automatic fill valves. All pools are required to be fully covered by a pool cover to limit evaporation.’ Stage 3 also states: ‘Prohibit the permitting of new swimming pools, Jacuzzi type pools, spas, ornamental ponds and fountain construction. Pools already permitted and under construction may be completely filled with water.’ Note the two teeth in Stage 3 that catch ordinary owners: AUTOMATIC FILL VALVES become non-compliant even though topping off by other means is allowed, and a POOL COVER becomes mandatory, not advisory. The plan defines ‘Swimming pool’ as ‘any structure, basin, chamber, or tank including hot tubs, containing an artificial body of water for swimming, diving, or recreational bathing, and having a depth of two
- feet or more at any point,’ so spas and hot tubs are squarely covered. Variances are available from the Water Director under section 4.4. B) DRAINING (year-round, independent of drought). Fort Worth Code of Ordinances section 12.5-302(b)
- makes it an affirmative defense to the MS4 discharge prohibition that the discharge was ‘Drainage from a private residential swimming pool containing no harmful quantities of chlorine or other chemicals. Drainage from swimming pool filter backwash is prohibited.’ So dechlorinated residential pool water may go to the storm sewer, but FILTER BACKWASH MAY NOT, ever. That defense also disappears under 12.5-302(c) if the director determines the discharge is a pollutant source, gives written notice, and the discharge continues.
Rules change and enforcement varies — confirm with your water provider before draining or refilling. Nothing here is legal advice.
Worth a look next door
- Filling a pool in San Antonio — Same state, different water: San Antonio fills at about 300 mg/L against 129 here.
- Filling a pool in Las Vegas — The other end of the scale: Las Vegas gets about 0.4 pool volumes of top-off against 2.1 pool volumes here.
Source: Fort Worth 2025 Water Quality Report web edition (canonical page; PDF: fortworthtexas.gov/files/assets/public/v/1/water/documents/drinking-water/wqr/2025-wqr_web.pdf) (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.