Filling a Pool in Anaheim: Your Tap Water’s Starting Numbers
Filling a pool in Anaheim means starting from Anaheim Public Utilities’s water — which is very hard at roughly 296 mg/L total hardness (about 17.3 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 Anaheim Public Utilities numbers index at +0.87 — firmly scale-forming (how this is calculated). That is the most scale-forming fill water of the 15 cities in this lookup that publish enough to compute it.
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 +0.87 — comfortably on the scaling side even after the correction. What it does settle is which mistake costs money in Anaheim. 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 Anaheim hardness every time. Replacing one full pool volume through top-off adds roughly another 296 ppm; starting from a fresh fill at about 296 mg/L, that reaches the 400 ppm ceiling after about 0.3 pool volumes of make-up water — less than one full pool volume — a hot-summer pool can work through that in a season or two, not decades. That is the 3rd 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
Anaheim Public Utilities reports hardness spanning 162 to 431 mg/L — a 2.7x range end to end. That is not measurement noise. It is what blending different sources into different service zones does over a year, and it means the single number at the top of this page is an average your own tap may not match. A pool a few neighbourhoods away can legitimately fill at a different hardness than yours. Test what comes out of your hose; do not plan off the midpoint.
Why Anaheim water is like this
Anaheim’s tap is hard because two of its three supply streams pick up minerals before they arrive, and the city’s own report breaks the chemistry out by stream (2024 data). GROUNDWATER: hardness 318 mg/L as CaCO3, total alkalinity 180 mg/L, pH 7.9, calcium 97 mg/L, magnesium 18 mg/L, bicarbonate 229 mg/L. LENAIN plant (treated imported): hardness 288 mg/L, alkalinity 140, pH 7.5, calcium 69, magnesium 28. MWD (fully treated imported): hardness 271 mg/L, alkalinity 116, pH 8.2, calcium 68, magnesium 26.
So the LOCAL groundwater is the hardest and by far the highest-alkalinity source – the opposite of the usual assumption that imported Colorado River water is the villain. The reason is geology plus recharge: the OCWD basin is recharged by the Santa Ana River, which drains the inland San Bernardino/Riverside watershed and arrives carrying dissolved calcium and bicarbonate, plus recycled water and imported water percolated into the same basin.
That is why Anaheim groundwater runs about 47 mg/L harder and 64 mg/L higher in alkalinity than the MWD water. TREND THAT MATTERS: in 2024 Anaheim completed what its General Manager calls "one of the largest groundwater treatment systems in the United States" to remove synthetic chemicals (PFAS) from the local basin.
Two treatment paths feed the city besides raw groundwater. Anaheim’s own Lenain Water Treatment Facility treats imported raw water from Walnut Canyon Reservoir (2024 combined filter effluent: highest single turbidity 0.48 NTU, 99 percent of samples under 0.3 NTU). MWD supplies fully treated water separately (0.06 NTU, 100 percent under 0.3 NTU).
The report shows a chlorine residual averaging 1.0 mg/L (range ND to 2.6) and attributes the disinfection byproducts to "Byproducts of Chlorine Disinfection"; it does not report a chloramine or ammonia residual. NO lime softening is reported – nothing in the treatment train removes hardness, which is why the calcium arrives at the tap intact. The 2024 PFAS groundwater treatment system is a contaminant-removal build, not a softening build; wells above the PFAS Response Level were removed from service.
NOTE for saltwater-pool owners: chlorine (rather than chloramine) residual means the fill water’s own disinfectant dissipates faster, but it does not change calcium or alkalinity at all.
Substantial, and the utility publishes the spread. Against averages of 318 (groundwater) / 288 (Lenain) / 271 (MWD) mg/L hardness, the citywide RANGE OF DETECTIONS for total hardness is 135 to 431 mg/L as CaCO3 (8.0 to 25 grains per gallon), and total alkalinity ranges 105 to 249 mg/L. That is roughly a 3x swing in hardness depending on which stream is feeding your neighborhood and when. pH ranges 7.1 to 8.2 and sodium 43 to 117 mg/L across the same sampling.
The mix is operational, not seasonal-by-calendar: Anaheim blends groundwater, Lenain-treated imported water, and fully treated MWD water, and shifts the proportions based on cost and availability. The 2024 completion of the PFAS groundwater treatment system is an explicit move toward more groundwater, so a homeowner testing in 2023 and again in 2026 could legitimately get different numbers from the same tap.
Practical implication: do not trust a single published citywide average for fill-water planning in Anaheim – test the actual fill.
Background sources: anaheim.net, pw.oc.gov, water.ca.gov.
Worth a look next door
- Filling a pool in Sacramento — Same state, different water: Sacramento fills at about 83 mg/L against 296 here.
- Filling a pool in Corpus Christi — The other end of the scale: Corpus Christi gets about 1.4 pool volumes of top-off against 0.3 pool volumes here.
Source: City of Anaheim Water Quality Report 2026 (based on 2025 data) (2026 (CY2025 data) 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.