Phoenix Hard Water Guide

How often should you drain your pool in Arizona?

Desert sun pulls water out of a pool every day, and the minerals stay behind. Here is how that shapes a drain-and-refill decision, and what Phoenix allows when you do it.

Why Arizona pools get harder every year

How often should you drain your pool? In Arizona the answer is driven by evaporation. When water evaporates, the calcium and magnesium stay behind; as the U.S. Department of Energy puts it, “When water evaporates, it leaves behind scale and mineral deposits.” Each top-up brings more minerals, all summer.

The starting point is already high. The City of Phoenix’s yearly water quality report for 2025 puts the hardness of city tap water at 172 to 302 parts per million (10 to 17.6 grains per gallon). Our page on Phoenix water hardness explains why that range moves through the year.

How often should you drain your pool in Arizona?

The City of Phoenix answers this in its water services FAQ: “To save water, pool draining should be infrequent (every five years plus years). Keeping chemicals in balance helps you avoid wasteful dumping of water.” The same answer mentions newer equipment that cleans calcium out of pool water and returns it to the pool.

The city gives no exact date. What decides it is the water itself:

  • Test calcium hardness. A pool test kit or a pool shop test reports it in parts per million.
  • Watch the trend. If each test reads higher than the last, evaporation and top-ups are concentrating minerals faster than rain, splash-out and backwashing remove them.
  • Ask a pool professional to read the result. The right range depends on your pool’s surface, equipment and chemistry. When the water can no longer be kept in balance, a partial or full drain and refill is the usual fix.

Calcium hardness limits: the CDC’s code for public pools

The U.S. Centers for Disease Control and Prevention publishes a model health code for public pools and spas (2024 edition). It is written for public pools, not home pools, but it is the clearest published yardstick:

  • Upper limit: “Calcium hardness shall not exceed 2500 ppm (mg/L).”
  • Testing: calcium hardness “shall be tested monthly at all AQUATIC VENUES.”

The code’s annex says 200 to 400 ppm “is preferred” (100 to 200 ppm for water warmer than 90°F) and that too much calcium causes cloudiness and scale. It adds that the 2,500 ppm ceiling “might not be appropriate for regions with particularly hard source water.” These are public-pool rules; for a home pool, treat them as a guide and follow your pool professional.

Calcium hardness in pools: what you see

Calcium hardness in pools shows as a pale crust at the waterline and on tile: mineral scale, the same thing the City of Phoenix says hard water leaves on plumbing fixtures. Our hard water stain removal page explains how scale is lifted, but on a pool surface follow your builder’s or surface maker’s cleaning instructions first.

Pool drain and refill: City of Phoenix rules

The City of Phoenix Water Services Department sets out how to drain a pool legally. Its rules, in plain words:

Where can I drain my pool water?

  • Reuse it first. For backwash or a small amount, the city says to “reuse the water to irrigate landscaping.”
  • A whole pool goes to the sewer clean-out. “If you have to drain a large amount of water - such as emptying the whole pool - put it down the home’s sewer clean-out.” The clean-out is the capped pipe, usually near the house, that gives access to your home’s sewer line.
  • Keep the flow low. “The maximum recommended discharge rate is 12 gallons per minute (720 gal/hr).” The city adds that a pump running at about 700 gallons an hour is about the right size.
  • Don’t make the hose permanent. The city warns that a permanent pool drain line may break plumbing code or county health rules and could contaminate the water when you refill.

Can I drain my pool into the street?

No. The city says: “Do not drain water into the street, alleyway or other city of Phoenix right of way.” Its Water Services questions page adds that under City Code Chapter 32C, pool water may not go into the storm drains. The city’s flyer also says not to drain into a septic tank, onto a neighbor’s yard or into a nearby wash.

What if you have no sewer clean-out?

Homes on septic tanks may not have one. In that case the city allows discharge into the right of way only with a permit, and only if the water is clean: dechlorinated and free of pollutants, with chlorine under 1 part per million and a flow under 50 gallons a minute. Two things are never allowed, even with a permit: discharging backwash (dirty filter water) and discharging water from saltwater pools. Draining into an alley is also prohibited.

When to drain a pool in Phoenix

Phoenix’s drain rules don’t name a season, though its rates favor winter (below). At 12 gallons a minute, most pools take a day or more to empty. Ask your pool professional how long your shell can safely stand empty.

What the refill water costs in Phoenix

Your city bills refill water like any other water you use. The City of Phoenix’s rate schedule effective March 1, 2025 charges inside-city homes per unit of 100 cubic feet (CCF), and 1 CCF is 748 gallons:

Billing months Water charge per CCF Plus environmental charge per CCF Total per CCF
January, February, March, December $4.93 $0.62 $5.55
April, May, October, November $5.65 $0.62 $6.27
June, July, August, September $6.13 $0.62 $6.75

The formula: pool gallons ÷ 748 × the total per CCF for that month.

Example (our calculation, not a city figure): an 18,000-gallon pool is about 24.1 CCF. At the City of Phoenix’s 2025 rates, that works out to about $134 in December to March, $151 in the spring and fall months, and $162 in summer, before taxes and fees. Outside-city rates are higher.

The city suggests refilling in the January, February or March billing cycles, when rates are lowest; since your sewer charge is based on those months, ask for a Sewer Fee Review if you do. Other Valley cities bill differently, so check your own water bill.

Refilling with hard tap water

A fresh fill resets the minerals to whatever comes out of your tap, which in Phoenix is already very hard. Whether to fill from a softened line is a question for your pool professional, because pool chemistry is balanced differently from drinking water. Our guide to whether Phoenix tap water is safe separates hardness from safety.

Where these facts come from

Common questions

How often does a pool get drained?
Not often. The City of Phoenix's water services FAQ says draining should be infrequent, "every five years plus years," and that keeping chemicals in balance avoids wasteful dumping. Test calcium hardness regularly; the reading tells you when the water can no longer be kept in balance.
Can I drain my pool into the street?
Not in Phoenix. The City of Phoenix says not to drain pool water into the street, an alleyway or other city right of way, and City Code Chapter 32C bars pool water from the storm drains. Use the sewer clean-out at your house, or reuse the water on your landscaping.
How long does it take to drain a pool at 12 gallons a minute?
Twelve gallons a minute is 720 gallons an hour. Divide your pool's volume in gallons by 720 to get the hours. A pool holding 18,000 gallons, for example, would take about 25 hours.
How much does it cost to drain and refill a pool?
The water part can be estimated from your city's rates. At the City of Phoenix's rates effective March 2025, our calculation for an 18,000-gallon refill inside the city is about $134 in January to March and about $162 in June to September, before taxes and fees. No official source gives a figure for labor, so ask more than one pool company for a written quote.