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Off-Grid Water Calculator — Collection, Storage & Filtration

Calculate daily water needs, collection capacity, storage requirements, and filtration for off-grid living

Daily Need

220 GPD

Collection

69.6 GPD

Storage

6,600 gal

Balance

-150.4 GPD

Daily Water Balance

-150.4 GPD

Deficit — additional source needed

Need

220 GPD

Collect

69.6 GPD

Storage Required

Total Storage6,600 gal
275-gal IBC Totes24 ($2,880)
1,000-gal Tanks7 ($4,200)

Filtration

Filter Units4
Filter Cost$600

Example Calculations

1Family of 4 with Goats, Moderate Climate

Inputs

People4
LivestockGoats (~10 GPD)
Garden400 sq ft
ClimateModerate (40 in/yr)
Roof1,200 sq ft

Result

Daily Need230 GPD
Collection69.5 GPD avg
Storage (30 days)6,900 gal
IBC Totes26

Human: 4 x 50 = 200 GPD. Goats: 10 GPD. Garden: 400 x 0.05 = 20 GPD. Total: 230 GPD. Roof: 1200 x 40 x 0.623 x 0.85 / 365 = 69.5 GPD avg. Storage: 230 x 30 = 6,900 gal.

2Couple with Chickens, Wet Climate

Inputs

People2
LivestockChickens (~5 GPD)
Garden200 sq ft
ClimateWet (55 in/yr)
Roof1,000 sq ft

Result

Daily Need115 GPD
Collection79.9 GPD avg
Storage (30 days)3,450 gal

Human: 2 x 50 = 100 GPD. Chickens: 5 GPD. Garden: 200 x 0.05 = 10 GPD. Total: 115 GPD. Collection: 1000 x 55 x 0.623 x 0.85 / 365 = 79.9 GPD.

Frequently Asked Questions

Q

How much water does an off-grid household need per day?

An off-grid household typically uses 50 gallons per person per day, which is about half the 80–100 GPD average for grid-connected homes. A family of 4 needs approximately 200 GPD for indoor use. Add 5–30 GPD for livestock and 0.05 gal/sq ft/day for garden irrigation during growing season.

  • Conservative indoor use: 50 gallons per person per day
  • Flushing toilet: 1.6 gal/flush, composting toilet: 0 gal
  • Shower: 2 gal/minute, 5–minute shower = 10 gal
  • Chickens: ~5 GPD total flock, Cattle: ~30 GPD per head
  • Garden: ~0.05 gal per sq ft per day during growing season
Q

How much rainwater can I collect from my roof?

A 1,000 sq ft roof in an area with 40 inches of annual rainfall can collect roughly 21,000 gallons per year. The formula is: Roof area (sq ft) x Annual rainfall (inches) x 0.623 x 0.85 efficiency factor. Actual collection varies by roof material and gutter efficiency.

  • Metal roof: 95% collection efficiency
  • Asphalt shingle: 85% efficiency (some absorption)
  • 1" of rain on 1,000 sq ft = 623 gallons
  • 40" annual rain on 1,200 sq ft roof = ~25,000 gal/year
  • First-flush diverter wastes first 1 gal per 100 sq ft per rain event
Roof SizeWet Climate (50"/yr)Moderate (40"/yr)Dry (22"/yr)
800 sq ft21,200 gal16,900 gal9,300 gal
1,200 sq ft31,700 gal25,400 gal13,900 gal
1,600 sq ft42,300 gal33,900 gal18,600 gal
Q

How much water storage do I need off-grid?

Plan storage for your longest expected dry spell. If your household needs 250 GPD and the longest dry spell is 30 days, you need 7,500 gallons of storage minimum. Common storage: 275-gallon IBC totes (~$120 each) or 1,000-gallon poly tanks (~$600 each).

  • Storage formula: Daily need x Dry spell days
  • 275-gal IBC totes: $100–$150 each, stackable
  • 1,000-gal poly tanks: $500–$700 each
  • 2,500-gal underground cistern: $2,000–$4,000 installed
  • Keep tanks shaded and covered to prevent algae growth
Q

What water filtration works best off-grid?

For drinking water, a multi-stage system works best: sediment filter, followed by activated carbon, then UV or ceramic for pathogen removal. Slow sand filters are the most cost-effective DIY option at ~$150, processing 50 GPD. Berkey-style gravity filters are popular at $350 but only process 25 GPD.

  • Slow sand filter: ~$150 DIY, 50 GPD, removes bacteria and sediment
  • Ceramic gravity filter: ~$80, 15 GPD, good for small households
  • Berkey-style: ~$350, 25 GPD, removes 99.99% of pathogens
  • UV purifier: ~$250, 200 GPD, kills bacteria and viruses
  • Always test water annually for bacteria, nitrates, and minerals

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Last Updated: Mar 20, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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