TL;DR
A standard residential pool holds 10,000-20,000 gallons of water. It is not drinkable as-is due to chlorine, algaecides, and other chemicals, but it can be treated for drinking with the right steps: dilute the chemical concentration by letting chlorine off-gas, filter through activated carbon to remove remaining chemicals and algaecides, then treat for any pathogens introduced after the pool was last treated. Approximately 90% of US homes with pools are within 1 mile of any given suburban neighborhood — this is a real emergency water resource.
Saltwater pools cannot be treated for drinking using the methods in this guide. Salt removal requires distillation or reverse osmosis. Do not attempt to drink from a saltwater pool without distillation.
The Chemical Reality of Pool Water
A well-maintained pool at the start of an emergency contains:
- Chlorine: 1-3 ppm (safe for drinking up to 4 ppm per WHO; 1-3 ppm is near the acceptable range but with other chemicals present, treatment is still advisable)
- Cyanuric acid (stabilizer): 30-80 ppm in outdoor stabilized pools. This is the primary concern — cyanuric acid is not removed by standard filtration and in higher doses has unknown long-term health effects
- Algaecides: Quaternary ammonium compounds or copper-based products — toxic at elevated concentrations
- pH adjusters: Muriatic acid or sodium carbonate — these change pH but don't persist as harmful compounds once pH is balanced
- Phosphate removers, clarifiers, enzymes: Various compounds in small quantities
As days pass after grid-down, unmaintained pool water degrades:
- Chlorine off-gasses rapidly in sunlight (half-life of about 2 hours in direct sun)
- Algae begins to grow within 3-5 days without chlorine
- Insects and animals begin using the pool as a water source
- Organic debris accumulates
The treatment approach differs depending on how long the pool has been sitting.
Freshly Maintained Pool Water (Days 1-5)
This is the cleanest scenario. The pool was recently treated and still has residual chlorine.
Treatment steps:
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Let it sit in sunlight in open containers: Fill clean containers and leave in direct sunlight for 2-4 hours. UV light rapidly breaks down residual chlorine and many organic compounds. This step is optional but reduces the chemical load before filtering.
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Filter through activated carbon: This is the critical step for pool water. Carbon adsorbs cyanuric acid, algaecide residues, and chlorine byproducts. A carbon column filter with 2-3 cups of activated carbon handles several gallons per pass. For a family needing 10-15 gallons per day, this is manageable with a dedicated filter setup.
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Test the filtered water: If you have test strips, check for residual chlorine (should be below 1 ppm after carbon filtration), pH (should be 6.5-8.5), and cyanuric acid if your strips test for it.
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Boil or chemically disinfect: The pool has likely been a sterile environment, but after grid-down, it has been open to the environment. Boil for 1 minute or treat with 2 drops of unscented household bleach per gallon (the pool water's residual chlorine may have off-gassed; this step ensures biological safety).
Degraded Pool Water (Days 6+)
Green, algae-laden water requires more aggressive treatment.
Additional steps before the process above:
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Coagulate: Add 1/4 teaspoon of alum (aluminum sulfate) per gallon of water. Stir and allow 30-60 minutes to settle. The alum causes suspended particles, algae cells, and much organic material to clump and sink.
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Settle and decant: Pour off the clearer upper portion, leaving the sediment. Aim for the top 60-70% of the container.
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Pre-filter: Strain through a cloth, then a coffee filter, to remove remaining particulates.
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Proceed with the standard treatment steps above.
Algae-laden water has higher organic load, which means your carbon filter will saturate faster. Plan to refresh the carbon media more frequently.
Volume Calculations
A 15,000-gallon pool provides approximately:
| Consumption Rate | Family of 4 | Duration | |-----------------|-------------|----------| | 1 gal/person/day (drinking only) | 4 gal/day | 3,750 days (10+ years) | | 2 gal/person/day (drinking + cooking) | 8 gal/day | 5+ years | | 5 gal/person/day (drinking + cooking + hygiene) | 20 gal/day | 2 years |
The limiting factor is not the pool volume — it is your treatment capacity. A single carbon filter run several times per day handles 10-20 gallons. For higher volume needs, build multiple parallel carbon filter columns.
Hot Tub Water
Higher chemical concentrations, smaller volume (typically 250-500 gallons), and often saltwater variants make hot tubs a last resort.
For non-salt hot tubs:
- Allow the water to cool completely (hot water accelerates chemical reactions and reduces treatment effectiveness)
- Hot tubs often have higher cyanuric acid and algaecide concentrations — double the carbon filtration pass (run through the filter twice)
- Higher chlorine shock treatments may have been used — allow 24 hours of sunlight exposure to off-gas before treatment
- Follow the full pool water treatment sequence
For salt hot tubs: The salt concentration is too high for filtration-based treatment. Do not use without distillation.
Neighbor Pool Considerations
In an extended emergency, approach neighbors about sharing their pool as a water resource. A community pool represents a multi-year water supply for a small group.
A reasonable community water management plan:
- Designate one person to manage chemical levels (if any remaining chemicals are available) to keep algae growth controlled
- Cover the pool when not in use to reduce evaporation and contamination
- Establish a collection schedule so multiple families can draw water in an organized way
- Maintain the treatment chain (coagulate, filter, boil) as a community standard
What Pool Water Cannot Become
Safe directly from the tap: Chemical load too high without treatment. Safe after simple boiling alone: Boiling does not remove cyanuric acid, algaecides, or other dissolved chemicals. Safe from a saltwater pool: Salt cannot be removed without distillation.
Use pool water as one element of your emergency water strategy — not as a substitute for stored water, but as the supplemental source that extends your supply indefinitely when combined with proper treatment.
Pro Tip
A pool test kit is worth adding to your emergency supplies for two reasons. First, it tells you the actual chlorine and chemical levels in pool water you are treating — you might find a freshly maintained pool with only 1 ppm chlorine that requires minimal treatment. Second, after a prolonged emergency, you will want to know when your remaining treated water supply's chlorine residual has dropped below safe levels. Test strips cost $8-15 and last for years.
Sources
Frequently Asked Questions
Can you drink pool water directly?
Probably not safely. Pool water typically contains 1-3 ppm of chlorine (sometimes higher), algaecides, pH adjusters, and potentially cyanuric acid stabilizer. At typical pool chlorine levels, the water is safe to use for cooking and most hygiene uses, but the chemical load — especially with algaecides and stabilizers — makes it inadvisable for regular drinking. Proper treatment reduces chemical load to safe drinking levels.
Is hot tub water more dangerous than pool water?
Yes. Hot tubs operate at much higher chemical concentrations (3-5 ppm chlorine or more, plus shock treatments, algaecides, and enzyme treatments) and at elevated temperatures that accelerate chemical reactions. Hot tub water should be treated as a last resort, and treated more aggressively than pool water. Allow it to cool first, then use the full treatment protocol.
How much water does a typical pool hold?
An average residential pool holds 10,000-20,000 gallons. At 1 gallon per person per day, a 15,000-gallon pool supplies a family of four for over 10 years. This is a significant emergency water asset — the limiting factor is purification capacity and fuel for treatment, not volume.
What about saltwater pools?
Saltwater pools are not actually filled with saltwater — they use a salt chlorinator to generate chlorine from a low-salt solution. The salt concentration is typically 2,500-3,500 ppm — about 10x lower than seawater but significantly above the 250 ppm maximum for drinking water. Salt removal requires distillation or reverse osmosis. Saltwater pool water cannot be made safe for drinking by filtration and chemical treatment alone.