Filling a Pool in Phoenix: Your Tap Water’s Starting Numbers
Filling a pool in Phoenix means starting from City of Phoenix Water Services Department’s water — which is very hard at roughly 237 mg/L total hardness (about 13.9 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 City of Phoenix Water Services Department numbers index at +0.43 — inside the balanced band (how this is calculated). That puts Phoenix 8th 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, +0.43 is a ceiling and the true figure sits at or below it — which for a near-balanced reading means Phoenix 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 Phoenix hardness every time. Replacing one full pool volume through top-off adds roughly another 237 ppm; starting from a fresh fill at about 237 mg/L, that reaches the 400 ppm ceiling after about 0.7 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 8th 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
City of Phoenix Water Services Department reports hardness spanning 172 to 302 mg/L — a 1.8x 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 Phoenix water is like this
Phoenix does not have one water – it has at least two chemically different source waters (CAP/Colorado vs SRP/Salt-Verde) landing at five separate treatment plants that are never blended into a single uniform product. That is why the published aesthetic ranges are so wide rather than a single figure: total hardness 172-302 ppm (10-17.6 grains), TDS 464-716 ppm, alkalinity 121-167 ppm, sodium 91-183 ppm, pH 6.6-8.8, temperature 47-92 F.
The mineral load itself is geological: snowmelt-origin river water crosses desert watersheds and dissolves calcium, magnesium and salts on the way down. Critically, the four treatment steps Phoenix documents are screening/presedimentation, coagulation-flocculation-sedimentation (ferric chloride), filtration, and disinfection (chlorine plus fluoride) – there is NO softening step, so calcium and alkalinity arrive at the tap essentially as the rivers delivered them.
The report states plainly that taste, odor and hardness are not regulated under drinking water health standards and are aesthetic aspects only. For a pool owner this means fill water already carries a large fraction of the calcium hardness and total alkalinity a pool needs, and because a Phoenix pool is topped off continuously against heavy evaporation, every top-off cycle leaves those minerals behind and drives CH, TA and TDS upward over the life of the water.
Conventional surface-water treatment with no softening: large-particle screening and presedimentation, coagulation/flocculation/sedimentation using a chemical coagulant such as ferric chloride, filtration, then disinfection with chlorine plus added fluoride. The absence of a lime-softening step is the reason hardness passes through. Phoenix’s 2025 report also discloses a Tier 3 CCR notification: in May 2025 the city collected 359 instead of the required 360 routine coliform/E. coli/chlorine samples. No E.
coli was found and chlorine levels were within EPA limits.
Yes, on both axes, though Phoenix does not publish a plant-by-plant or ZIP-by-ZIP hardness table. Seasonally, the report documents that algae growing in the canals during late summer and fall are a major source of a musty odor and taste, and records a delivered-water temperature range of 47-92 F – a swing that matters for fill-water volume and for how fast a newly filled pool equilibrates.
Background sources: phoenix.gov, azmet.arizona.edu, amwua.org.
Before you drain or refill in Phoenix
Substantial and specific. DRAINING: Phoenix’s official flyer directs owners to irrigate landscaping with pool discharge or to drain/backwash into the home’s sanitary sewer clean-out at a maximum recommended discharge rate of 12 gallons per minute (720 gal/hr), less if the drain line is small or in poor condition, checking immediately for backups into showers and tubs.
Explicit prohibitions: do NOT backwash or drain into the street; do NOT let pool water drain onto neighboring yards or into nearby washes; do NOT drain into a septic tank; do NOT install the pool drain line as a permanent fixture (may violate city plumbing code or county health regulations and could contaminate the water when you refill).
PERMIT: if you have no sewer clean-out (for example a septic home) and the pool water is clean (de-chlorinated and free of pollutants), you can discharge it into the right-of-way only if you have a discharge permit, obtained via the city’s esd_discharge_request form. REFILL / BILLING: Phoenix sewer fees are recalculated each year effective July based on a percentage of average water used during the January, February and March billing periods, so a winter pool fill can inflate your sewer charge for a full year.
Phoenix explicitly lists ‘pool fills during the January, February, or March billing periods’ as a qualifying condition for a Request for Sewer Fee Review under Phoenix City Code 28-35(d); the request must be submitted within 60 days of the July bill date and PCC 28-35 states exceptions will not be granted past that. DROUGHT: Phoenix has been in a Stage 1 Water Alert since June 2022 under its Drought Management Plan (Phoenix City Code Chapter 37, Sections 121-130.2).
Stage 1 is public education and voluntary conservation only – residential pool filling is NOT restricted. The 2021 Drought Management Plan mentions pools exactly once, and only to note that city facilities such as parks and community pools may be impacted; it places no restriction on filling a private pool. The city does state that if future restrictions become necessary, more severe stages may include requiring child-safe pool covers to reduce evaporation.
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 Mesa — Same state, different water: Mesa fills at about 290 mg/L against 237 here.
- Filling a pool in Orlando — The other end of the scale: Orlando gets about 2.1 pool volumes of top-off against 0.7 pool volumes here.
Source: City of Phoenix 2025 Water Quality Report (Consumer Confidence Report), main system (2025 report data), accessed 2026-08-10. 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.