Well Water Storage Calculator
Created by: Natalie Reed
Last updated:
Size atmospheric storage for wells with outage coverage, safety factor, and pump flow needed to recover storage in your chosen refill window.
Well Water Storage Calculator
UtilityApplicationWhat is a Well Water Storage Calculator?
A well water storage calculator sizes an atmospheric storage tank to cover household demand, livestock, and outage duration. It also estimates minimum pump capacity to refill storage during non-peak hours.
Daily demand = (people × gppd) + extra uses
Storage = (daily demand ÷ 24 × outage hours) × safety
Pump gpm = Storage ÷ refill window (minutes)
How It Works
Enter people count, per-person gallons, outage hours, and any livestock/irrigation demand. The calculator computes needed storage volume with a safety buffer and estimates pump flow required to recover storage in a chosen refill window (default 6 hours).
Common Applications
- Plan cistern capacity for slow-recovery wells so showers and laundry never outrun supply.
- Size emergency storage for wildfire or storm outages alongside generator runtimes.
- Combine household, livestock, and irrigation demands into one storage target with safety margin.
- Check if existing pumps can refill storage overnight by comparing gpm needs to pump curves.
- Estimate total system storage (pressure tank + cistern) when upgrading fixtures or adding a rental unit.
Example Calculation
Sizing Tips
- Add 10-20% safety for summer irrigation or peak guests.
- Use food-grade tanks; protect from UV if outdoors.
- Include a float switch and overflow for reliable pump control.
- Pair storage with an appropriately sized pressure tank and booster pump if needed.
Frequently Asked Questions
Why add a storage tank to a well system?
Storage increases available water during peak household use, adds a buffer for outages or low recovery wells, and reduces rapid pump cycling that can shorten pump life. A correctly sized atmospheric tank plus pressure tank smooths demand spikes and lets you schedule recovery pumping during off-peak hours.
How big should my well pressure tank be?
Rule of thumb: pick a pressure tank with at least one minute of pump runtime drawdown so the pump cycles less often. For larger buffers (showers, laundry, livestock), an atmospheric storage tank is more efficient. This calculator sizes the storage portion; pressure tank selection still matters for day-to-day pressure stability.
What outage duration should I plan for?
Many homes plan for 12–24 hours of coverage to ride through pump faults or short power outages. Off-grid, wildfire-prone, or boil-water regions often plan for 48 hours or more. Add a safety factor for summer irrigation or guest weekends to avoid dry taps.
How do I estimate household demand?
Typical homes use 60–100 gallons per person per day depending on fixtures, leaks, and lifestyle. Add irrigation, livestock, and any fire reserve. If you do laundry at home or run dishwashers daily, use the higher end; efficient fixtures and short showers trend toward the lower end.
Do I need a contact time for chlorination?
Yes. Chlorination requires sufficient contact time (CT) to inactivate pathogens. Storage tanks can provide this time, but local codes specify volume and baffling. Consult local health departments and follow NSF-rated components to ensure contact time before water reaches fixtures.
Can I bury a poly tank?
Only tanks rated for burial or partial burial should go underground; most atmospheric poly tanks are for above-ground use. Buried tanks need engineered backfill, venting, and access for cleaning. Always follow manufacturer specs and local codes to avoid collapse or contamination risk.
Related Calculations
Use these tools to round out water and utility planning.
- Rainwater Harvesting Calculator — supplement wells with roof catchment volume estimates.
- Livestock Water Trough Sizing Calculator — align trough reserve with cistern capacity for herds.
- Firewood Needs Calculator — plan power-outage heating when pumps are offline.
Sources and References
- US EPA, "Public Water System Guidance Manual: Small Systems," 2025.
- Goulds Water Technology, "Residential Water System Sizing Guide," 2024.
- University Extension, "Rural Water System Design Guidelines," Bulletin 2025.
- National Drinking Water Alliance, "Household Water Use Benchmarks," 2025.