# Pool Evaporation in Phoenix: Why You're Losing a Quarter Inch a Day

If you've ever glanced at your Phoenix pool in July and thought, "that water level was higher yesterday," you're right. Phoenix pools lose water faster than pools almost anywhere else in the country. It's not always a leak. Most of the time it's just evaporation doing what evaporation does in a desert.

But evaporation in Phoenix is dramatic enough that a lot of homeowners mistake it for leaks, pay for leak detection they don't need, and waste water topping off more than necessary. Others underestimate how much evaporation is adding to their water bill, their calcium problem, and their chemistry drift.

This guide covers exactly how much water Phoenix pools lose to evaporation, how to tell evaporation from a real leak, what it's costing you, and what you can do about it.

## How Much Water Does a Phoenix Pool Actually Lose?

Evaporation rates vary dramatically by season. Rough numbers for an average 15,000-gallon Phoenix residential pool:

| Month | Daily Loss | Monthly Loss |
|---|---|---|
| January | 1/16 to 1/8 inch | 600 to 1,200 gallons |
| February | 1/8 inch | 900 to 1,500 gallons |
| March | 1/8 to 1/4 inch | 1,500 to 2,500 gallons |
| April | 1/4 inch | 2,500 to 3,500 gallons |
| May | 1/4 to 3/8 inch | 3,500 to 5,000 gallons |
| June | 3/8 to 1/2 inch | 5,000 to 7,000 gallons |
| July | 1/2 inch | 6,500 to 8,000 gallons |
| August | 3/8 to 1/2 inch | 5,500 to 7,500 gallons |
| September | 1/4 to 3/8 inch | 4,000 to 5,500 gallons |
| October | 1/4 inch | 2,500 to 3,500 gallons |
| November | 1/8 inch | 1,000 to 1,800 gallons |
| December | 1/16 to 1/8 inch | 700 to 1,200 gallons |
| **Annual total** | | **35,000 to 47,000 gallons** |

That's 2 to 3 times your pool's total volume leaving your backyard every year. To a pool owner in Seattle or Chicago, those numbers sound insane. To a Phoenix pool owner, they sound about right.

## What Drives Evaporation in Phoenix

Five factors control how fast water evaporates from a pool, and Phoenix has all five dialed to maximum for about 6 months of the year:

**Air temperature.** Hot air holds more water vapor than cool air. The hotter the ambient temperature, the more water the air will pull from the pool. Phoenix summer highs of 110 to 115°F drive evaporation rates that triple or quadruple cool-climate norms.

**Water temperature.** Warm water evaporates faster than cool water. Phoenix pool water regularly hits 90 to 95°F in summer, versus 75 to 80°F in pools elsewhere. Warm water + hot air is a double hit.

**Humidity.** Low humidity pulls water out of a pool faster. Humid air is already saturated and can't hold much more. Phoenix summer humidity averages 15 to 30% outside of monsoon, which is extremely low by national standards. Phoenix in July is drier than most US cities in January.

**Wind speed.** Wind strips evaporated water off the pool surface and replaces the air above the water with fresh dry air, accelerating the cycle. Phoenix afternoon winds (especially pre-monsoon dry wind) can double evaporation compared to still conditions.

**Direct sun exposure.** Sunlight heats the water surface directly, which adds to evaporation on top of air temperature effects. Phoenix averages 299 sunny days per year.

When all five peak together—hot air, warm water, low humidity, afternoon wind, direct sun—you can watch water disappear. A Phoenix pool in July can lose half an inch in a single afternoon if conditions are right.

## Evaporation vs Leak: How to Tell the Difference

This is the question we get asked the most. A Phoenix pool that's dropping an inch or more per week in summer might just be evaporating, or it might be leaking. Here's how to tell.

### The bucket test

The most reliable DIY diagnostic for a pool leak. Full procedure:

1. Fill a 5-gallon bucket about 3/4 full of pool water.
2. Place the bucket on the pool's top step so the inside water level is at the same level as the pool water.
3. Mark both water levels (inside the bucket and on the pool) with a grease pencil or tape.
4. Turn off any automatic water fillers.
5. Turn off the pump (optional - some tests are run with the pump on to isolate pressure-side leaks).
6. Wait 24 to 48 hours.
7. Measure the drop in each water level.

Interpretation:

- **Both dropped the same amount:** Evaporation only. No leak.
- **Pool dropped more than the bucket:** Leak. Call a pro.
- **Difference is over 1/4 inch in 24 hours:** Significant leak. Call immediately.

Run the test twice if results are ambiguous, once with the pump running and once without. A difference between those two tests suggests a pressure-side leak (plumbing lines after the pump).

### Red flags that suggest a leak, not evaporation

- Water level drops more than 1/2 inch per day for multiple days
- Soft or soggy ground around the pool or equipment pad
- Cracks in plaster, tile, or coping
- Air bubbles in pump basket (suction-side leak)
- Chemistry drifts constantly despite balanced starting point
- Equipment running but pressure gauge dropping
- Higher than normal water bill

### When evaporation alone explains the loss

- Daily loss in summer is 1/4 to 1/2 inch
- Daily loss in winter is 1/16 to 1/8 inch
- Bucket test matches pool loss
- No visible wet spots or cracks
- Loss increases in hotter weather and decreases in cooler weather
- Tracks with windy days

For most Phoenix pools, the answer ends up being evaporation. But a leak check is always worth ruling out before you accept 3/4 inch per day as normal.

## What Evaporation Is Actually Costing You

Three ways evaporation drains your wallet in Phoenix:

### 1. Water bill

Phoenix water rates vary by city and tier. Rough numbers:

- City of Phoenix: $2.50 to $5 per 1,000 gallons depending on tier
- Scottsdale: $3 to $6 per 1,000 gallons
- Mesa, Tempe, Chandler: $2 to $5 per 1,000 gallons
- Most private well owners: near zero variable cost

For a 15,000-gallon Phoenix pool losing 40,000+ gallons per year to evaporation, that's **$100 to $240/year in water cost just for evaporative losses.** Not catastrophic, but not nothing.

### 2. Chemistry drift

Every gallon of evaporated water leaves behind every dissolved solid: calcium, salt, CYA, total dissolved solids. Refill water brings in fresh calcium. Net effect: your pool concentrates minerals faster in Phoenix than anywhere else, which drives more frequent drain cycles (covered in our [hard water guide](/blog/phoenix-hard-water-pool-guide.html)).

Every gallon of chemistry drift you slow with reduced evaporation pushes your next drain back further.

### 3. Energy cost for the auto-fill valve

Most Phoenix pools have an automatic fill valve that opens when water drops below a set level. That valve pulls from your domestic water supply. If you're on a well with a pressurized tank, every fill cycle runs your well pump. Over a summer that adds $20 to $50 to your electric bill.

## How to Reduce Pool Evaporation

Here's what actually works, ranked by effectiveness:

### Pool cover (solar or automatic)

The single most effective thing you can do. Solar covers reduce evaporation by 50 to 95% depending on fit and quality. Automatic covers are even more effective (95 to 99%). They also:

- Reduce chlorine demand (UV can't reach the water)
- Retain heat overnight
- Keep debris out
- Reduce calcium concentration rate by 50%+

Drawbacks:

- Solar covers are ugly and require manual handling
- Automatic covers are expensive ($8,000 to $20,000 installed)
- Covers need to come off before swimming
- Hot Phoenix sun can make a covered pool too warm in July and August

For most Phoenix homeowners, a liquid solar cover (see below) is a better fit than a physical cover.

### Liquid solar cover

A chemical additive that forms a microscopic monomolecular film on the water surface. Reduces evaporation by 10 to 40%. Invisible, doesn't affect swimming, costs $10 to $20/month.

Drawbacks: works less well on windy days (the film gets broken up), needs to be added continuously, less effective than a physical cover.

Best used alongside other strategies.

### Windbreaks

If evaporation is severe and wind is a factor, partial wind protection (a privacy fence, hedge, or landscaping on the prevailing wind side) can cut evaporation 10 to 20%. Not typically worth doing just for evaporation, but worth considering if you're already landscaping.

### Lower water temperature

Counterintuitive advice for a pool owner, but: running the pump only at night (6 PM to 8 AM) instead of during the day keeps water temperature slightly cooler, which reduces evaporation modestly. Also saves on electric costs if you're on time-of-use billing.

In August when pool water can hit 95°F+, some homeowners actually use pool chillers to cool water back to the 85°F range. This is expensive and usually only makes sense for spa-attached pools or very hot pools.

### Pool shading (strategic landscaping)

Trees that shade the pool in afternoon can reduce water temperature by 3 to 5°F, which cuts evaporation 10 to 20%. Keep in mind:

- Roots and leaf drop near pools is a long-term maintenance issue
- Pick drought-tolerant native species (palo verde, acacia, desert willow)
- Shade the pool, not the solar equipment
- Allow 20+ feet between trees and pool edge

### Reduce water features

Waterfalls, sheer descents, fountains, and scuppers all dramatically increase evaporation by exposing more water surface to air and adding mechanical agitation. A single residential waterfall can triple the evaporation rate of the pool.

If you're not using water features, turn them off. Or automate them to run only during specific hours.

### Accept it

For many Phoenix homeowners, the cost of fighting evaporation ($50/month for chemicals + physical cover) is higher than the cost of just accepting it ($10 to $20/month in water). If you don't have a chemistry or cost problem, you might not have a problem.

## The Autofill Debate

Most Phoenix pools are plumbed with an automatic fill valve that keeps water level constant. Benefits:

- Prevents pump damage from low water
- Protects skimmer from running dry
- Keeps water level visually consistent

Drawbacks:

- Can mask leaks (water level never drops, so you don't notice)
- Adds water (and calcium) continuously
- Uses domestic water even when you're out of town

Recommendation: keep your autofill, but turn it off once per month for 24 hours to test water loss. If you lose more than an inch in 24 hours without the autofill, check for leaks.

## Phoenix Evaporation vs Other Cities

For context on how extreme Phoenix is:

| City | Summer Daily Evaporation | Annual Total (15k pool) |
|---|---|---|
| Seattle | 1/16 to 1/8 inch | 12,000 to 18,000 gal |
| Portland, OR | 1/16 to 1/8 inch | 12,000 to 18,000 gal |
| Chicago | 1/8 inch | 15,000 to 22,000 gal |
| Atlanta | 1/8 to 1/4 inch | 18,000 to 25,000 gal |
| Dallas | 1/4 inch | 25,000 to 35,000 gal |
| Los Angeles | 1/4 inch | 22,000 to 30,000 gal |
| Las Vegas | 1/4 to 1/2 inch | 30,000 to 40,000 gal |
| **Phoenix** | **1/2 inch** | **35,000 to 47,000 gal** |

Phoenix is roughly 2x Chicago, 1.5x LA, and 20% higher than Las Vegas. Only Palm Springs and similar desert pools lose more.

## When to Call for Help

Worth calling a pro if:

- Bucket test shows a leak (over 1/4 inch difference in 24 hours)
- Water level drops faster than seasonal norms
- You see soft spots or settling around the pool
- Equipment pad is wet or muddy
- Chemistry drifts constantly

Leak detection service runs $250 to $500 in Phoenix. Not cheap, but catching an underground plumbing leak early beats paying $2,000+ to dig up a pool deck later.

## When to Call Roadrunner

If your pool is dropping water faster than seems normal, we can diagnose whether it's evaporation or a real leak. If it's evaporation, we'll tell you that honestly and not sell you a leak detection service. If it's a leak, we can locate it and quote the repair.

For weekly service customers, water level monitoring is part of every visit. We catch sudden drops early, before they become problems.

Call **602-460-2221** or [request service online](/pool-repair-services.html).

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