Filling a Pool in El Paso: Your Tap Water’s Starting Numbers
Filling a pool in El Paso means starting from El Paso Water (El Paso Water Utilities – Public Service Board), PWS TX0710002’s water — which is hard at roughly 175 mg/L total hardness (about 10.2 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 El Paso Water (El Paso Water Utilities – Public Service Board), PWS TX0710002 numbers index at +0.04 — inside the balanced band (how this is calculated). That puts El Paso 14th 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, +0.04 is a ceiling and the true figure sits at or below it — which for a near-balanced reading means El Paso 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 El Paso hardness every time. Replacing one full pool volume through top-off adds roughly another 175 ppm; starting from a fresh fill at about 175 mg/L, that reaches the 400 ppm ceiling after about 1.3 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 15th 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
El Paso Water (El Paso Water Utilities – Public Service Board), PWS TX0710002 reports hardness spanning 63 to 236 mg/L — a 3.7x 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 El Paso water is like this
THE KEY FACT, and it is a quote straight out of EPWater’s 2025 Consumer Confidence Report: ‘Although some customers receive water from only one source, most customers receive water from two sources, DEPENDING ON THE TIME OF YEAR.’ El Paso is the one metro of these four where a pool owner’s fill water is a fundamentally different substance in July than in January. Here is the mechanism.
EPWater’s surface water plants can only run while the Rio Grande is delivering, and that is not a natural river season — it is an irrigation-release season governed by how much water is stored in Elephant Butte and how the 1939 Rio Grande Compact allocates it among Colorado, New Mexico and Texas.
That season is short and wildly variable: EPWater notes that in 2013 ‘river water was only available for less than two months’, and its own March 2019 CEO newsletter reported Elephant Butte at 10 percent of capacity (after a 2018 low of 3 percent) with ‘a May delivery of river water — two months later than normal.’ When the river is off or short, EPWater pumps groundwater instead: ‘Limited river water means groundwater is at a premium.
EPWater maximizes groundwater production by rehabilitating old wells and drilling new ones.’ Rio Grande surface water and deep bolson groundwater are not chemically similar — the bolson water is mineralized enough that part of it must be run through reverse osmosis to be potable at all. So the practical consequence: an El Paso pool topped off in one season may be receiving softer, lower-TDS treated river water, and in another season water dominated by groundwater and desalination blend.
EPWater’s own FAQ describes the result as ‘Water in El Paso is described as moderately hard to hard’ — a range, not a number, which is itself the tell. I did NOT verify specific El Paso hardness or TDS values; several sites that publish confident-looking El Paso hardness ranges are SEO content farms and their numbers should not be trusted.
The 2025 CCR states that El Paso runs one surface and two groundwater sources and that ‘some customers receive water from only one source, most customers receive water from two sources, depending on the time of year.’ Both axes are live: WHICH source you get depends on where you are in the city (Mesilla Bolson on the west, Hueco Bolson on the east, surface water from the Rogers and the two Canal plants), and HOW MUCH of each you get depends on the month and on Elephant Butte storage.
Turbidity is even reported separately per surface plant in the CCR (Rogers 0.16 NTU, Robertson Canal 0.38 NTU, Umbenhauer Canal 0.36 NTU), confirming the plants are operated and monitored as distinct streams. Magnitude of the hardness/TDS swing is NOT published by EPWater — I could not verify a number and will not invent one.
Background sources: epwater.org, cdnsm5-hosted.civiclive.com, gato-docs.its.txst.edu.
Before you drain or refill in El Paso
VERIFIED from EPWater’s own Drought Contingency Plan, with one important caveat about the document itself.
THE RULE: ‘No draining or filling pools (except to maintain levels for filter function).’ CAVEAT ON WHICH STAGE: this bullet sits in the mandatory-restriction list that appears under the heading ‘STAGE 3: Drought Warning’, but the prose introducing that same list reads ‘All mandatory requirements of Stage 1 shall remain in effect during Stage 2’ — EPWater’s plan has an internal off-by-one between its stage headings and its body text (the same defect repeats at the next heading, where ‘STAGE 4: Drought Action Stage’ is followed by ‘All requirements of Stage 2 shall remain in effect during Stage 3’).
So the restriction is real and quoted exactly, but a pool owner should confirm the operative stage with EPWater rather than rely on the plan’s stage labels. They are triggered by DEMAND AGAINST DELIVERY CAPACITY — Stage 1 when demand reaches or exceeds 85 percent of delivery capacity for 4 consecutive days; Stage 2 at 90 percent for 3 consecutive days; Stage 3 at 95 percent for 2 consecutive days; Stage 4 at 95 percent for 5 consecutive days.
That means an El Paso pool-fill restriction can arrive during a heat wave with full reservoirs, purely because everyone turned on their hose at once — precisely the weekend a pool owner wants to fill.
Also: EPWater discontinues variances ‘during water emergencies and drought Stages 2 and 3’, and at the Stage described as suspending permits, ‘All permits and variances will be suspended, and no new ones will be issued.’ YEAR-ROUND RULES that apply to pool work regardless of drought stage: no residential watering Mondays; EVEN addresses Tue/Thu/Sat, ODD addresses Wed/Fri/Sun; from April 1 to September 30 outdoor watering is prohibited between 10:00 a.m.
and 6:00 p.m.; and ‘Water flowing into the street’ is a listed water-waste violation, which is the provision that bites a pool owner draining or backwashing to the gutter. Violations: (915) 594-5508. IMPORTANT NEGATIVE FINDING: multiple third-party sites claim El Paso requires a PERMIT from El Paso Water to fill or refill a residential pool. I could NOT verify that anywhere in EPWater’s Drought Contingency Plan, its Rules and Regulations No.
5, its ordinance-and-enforcement page, its conservation pages or its FAQ, and it does not appear in any EPWater document I opened. Treat that claim as unsubstantiated. City Code Chapter 15.13 (Water Conservation) itself returned HTTP 403 from Municode and remains UNREACHABLE, not confirmed absent — so I cannot rule out an additional pool provision living in the ordinance text.
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 175 here.
- Filling a pool in Henderson — The other end of the scale: Henderson gets about 0.3 pool volumes of top-off against 1.3 pool volumes here.
Source: El Paso Water – Chemical Analysis, City Water (posted on epwater.org water-quality page); disinfectant from 2025 Drinking Water Report (CCR) (Chemical analysis doc dated 2017 per PDF metadata (still posted as current 2026); disinfectant residual from 2025 CCR (2025 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.