Filling a Pool with Well Water: Complete Guide

Using your well to fill a swimming pool can save hundreds of dollars compared to water delivery — but it's not without risks. Done wrong, you can burn out your pump, run your well dry, or turn your pool green. Here's how to do it right.

Pool Volume: How Much Water Are We Talking?

First, calculate how much water your pool holds:

Pool Type	Typical Gallons
Above-ground (15' round)	4,000-5,000
Above-ground (18' round)	7,500-8,500
Small inground (12x24)	8,000-10,000
Medium inground (16x32)	15,000-20,000
Large inground (20x40)	25,000-35,000

Calculator: Length × Width × Average Depth × 7.5 = gallons (for rectangular pools)

Can Your Well Handle It?

Calculate Fill Time

At different flow rates, here's how long a 20,000-gallon pool takes:

Well GPM	Hours to Fill	Days (8 hrs/day)
5 GPM	67 hours	8-9 days
10 GPM	33 hours	4-5 days
15 GPM	22 hours	3 days
20 GPM	17 hours	2-3 days

Critical Question: Recovery Rate

Your well's GPM rating is not sustainable flow. It's the maximum rate before the water level drops too low.

• High-yield well (15+ GPM): Can likely sustain continuous filling
• Medium-yield (8-15 GPM): Fill in sessions, let well recover
• Low-yield (under 8 GPM): Fill very slowly over many days, or consider water delivery

Protecting Your Well and Pump

Rule 1: Fill in Sessions

Unless you have a very high-yield well, don't try to fill continuously:

• Session length: 6-8 hours maximum
• Recovery time: Let well recover overnight (8-12 hours)
• Plan ahead: Start filling 1-2 weeks before you need the pool

Rule 2: Watch for Warning Signs

Stop filling immediately if you notice:

• Air sputtering: Pump is pulling air — water level dropped below pump
• Muddy/sandy water: Pump is near the bottom
• Pressure drop: Flow slowing significantly
• Pump running hot: Extended operation can overheat motors

If you see air or sediment, stop immediately and let the well recover for 24+ hours.

Rule 3: Don't Run Other Water

While filling, minimize other water use:

• Don't run irrigation while filling pool
• Time showers and laundry for recovery periods
• Consider your household's baseline needs

Well Water Chemistry for Pools

Well water often has characteristics that require adjustment before swimming:

Common Well Water Issues

Issue	Effect in Pool	Solution
High iron	Brown/orange staining when chlorine added	Metal sequestrant before chlorine
High copper	Green water, green hair staining	Metal sequestrant before chlorine
Hard water	Scale buildup on pool surfaces	Add scale inhibitor
Low pH	Corrosive to equipment	Add pH increaser
High pH	Cloudy water, scale	Add pH decreaser

The Metal Problem (Very Common)

Here's a scenario we hear often:

1. Fill pool with well water — looks clear
2. Add chlorine to sanitize — pool turns green or brown
3. Assume it's algae, add more chlorine — gets worse
4. Frustration ensues

What actually happened: Dissolved iron and copper (invisible in well water) oxidize when chlorine is added, creating visible discoloration.

Correct Approach

1. Test your well water for iron, copper, pH, and hardness before filling
2. Add metal sequestrant to the pool before adding any chlorine (follow product directions)
3. Let it circulate for 24 hours
4. Then add chlorine gradually
5. Balance chemistry (pH, alkalinity, calcium hardness)

Cost Comparison: Well vs. Water Delivery

Well Water Cost

• Electricity: ~$20-$50 for 20,000 gallons (depending on well depth and pump efficiency)
• Chemicals: Metal sequestrant adds ~$15-$30
• Total: $35-$80

Water Delivery Cost

• Per load: $200-$400 for 4,000-6,000 gallons
• 20,000 gallons: $800-$1,600 for 4-5 loads
• Pros: Fast, no stress on well, often pre-treated water

When Water Delivery Makes Sense

• Low-yield well (under 5 GPM)
• Need pool filled quickly
• High iron/metals in well water
• Recent pump replacement (avoid stressing new pump)
• During drought when well level is marginal

Step-by-Step: Safe Pool Filling

Before You Start

1. Know your well: GPM rating and recent performance
2. Test water: At minimum, know iron and copper levels
3. Calculate time: Pool gallons ÷ (GPM × 60) = hours needed
4. Plan sessions: Divide total time into 6-8 hour blocks

During Filling

1. Start a timer when you begin each session
2. Check periodically for air sputtering or pressure drops
3. Mark water level in pool to track progress
4. Stop on schedule — don't push it
5. Let well recover overnight before next session

After Filling

1. Add metal sequestrant first (if metals present)
2. Run filter for 24 hours
3. Add chlorine gradually
4. Test and balance chemistry
5. Wait for clarity before swimming

What If Something Goes Wrong?

Well Ran Dry / Pump Lost Prime

1. Stop all water use immediately
2. Wait 24-48 hours for well to recover
3. If pump won't start or runs but no water, call us — pump may have overheated

Pool Turned Green/Brown After Chlorine

1. Stop adding chlorine
2. Add metal sequestrant (double dose)
3. Run filter continuously
4. Backwash filter frequently
5. May take several days to clear

Taking Too Long / Well Can't Keep Up

Options:

• Supplement with water delivery for remaining volume
• Extend timeline with longer recovery periods
• Fill only to partial level for now