Emily ParkerBy Emily Parker

Updated November 2026

An off grid water storage system lets you keep a reliable supply of water on a property with no municipal connection, no well pump running on grid power, or both. In this guide you will work out how much storage you need, choose a tank and pump arrangement that matches your head height and flow rate, and avoid the mistakes that leave people short in dry weeks. The method is simple: estimate daily use, multiply by days of autonomy, then size the tank and the pump around that number.

Step 1: Calculate Your Daily Water Use

Start with real numbers rather than guesses. Typical household use in the US runs roughly 60 to 80 gallons per person per day, but off-grid homes that practice conservation often land lower. Add up each use: drinking and cooking, showers, toilet flushes, laundry, dishwashing, livestock and garden irrigation. Keep a notebook for a week, reading a water meter if you have one, to catch the uses you forget.

Shopping for one? See our guide: 6 Best Off Grid Water Purification System Options for Remote Living (2026).

Step 2: Decide How Many Days of Storage You Need

Storage is measured in days of autonomy, meaning how long the tank can supply you if the source stops, such as a dry spring, a frozen line or a failed pump. Three to five days is a common target for a home with a reliable source. If your source is rain catchment or a seasonal spring, plan for 30 days or more and size your collection area to match. Multiply daily use by days of autonomy to get your minimum tank volume, then add 10 to 20 percent of headroom.

Step 3: Match Tank Placement to Head Height and Flow Rate

Where the tank sits determines how you move water. A tank set higher than the fixtures can feed them by gravity, which needs no electricity. Each foot of elevation gives roughly 0.43 PSI of pressure, so a tank 20 feet above a tap delivers about 8.7 PSI before losses. If the tank sits lower than the fixtures, you need a pump sized for the total dynamic head, which is vertical lift plus friction loss in the pipe, at the flow rate you expect at peak use.

Choosing Between Gravity and Pumped Systems

  • Gravity feed: Best when you have natural elevation. Low maintenance, no power draw, but pressure is limited by the height difference.
  • Pressure pump with a pressure tank: Works from any storage location. Pump size depends on flow in gallons per minute and total head in feet.
  • Solar-powered pump: Pairs well with a storage tank because the tank buffers the pump’s intermittent output, so you pump during sun hours and draw from storage at night.

Step 4: Pick Tank Materials and Protect the Water

Food-grade polyethylene tanks are the most common choice for potable storage. They resist corrosion and are light enough to install without heavy equipment. Store the tank in shade or insulate it, since warm water encourages algae and bacterial growth. Vent the tank with a screened, insect-proof vent, and fit a sediment filter ahead of the house line. Potable water storage should also be followed by treatment; consult a licensed water professional or your local health department for testing and treatment requirements.

Checklist for Your Build

  1. Written daily-use estimate and days of autonomy target
  2. Tank volume with headroom, food-grade and opaque or shaded
  3. Measured elevation difference and pipe run length
  4. Pump flow rate (GPM) and total head (feet) calculated
  5. Sediment pre-filter, inlet screen and insect-proof vent
  6. Drain valve and overflow directed away from the foundation

Common Mistakes

  • Sizing the tank for average use instead of peak or dry-season use.
  • Ignoring friction loss, which can cut delivered flow noticeably on long runs of small pipe.
  • Leaving the tank exposed to sun, leading to algae and warm, unpleasant water.
  • Skipping winter protection for exposed pipes and the tank itself.
  • Forgetting an overflow path, which can erode soil or saturate the foundation.

For a full build sequence, see How to Build an Off Grid Water System: A Step-by-Step Guide, and if you plan to power the pump with panels, Off Grid 12V Water System: How to Plan, Size and Build One covers the electrical side. For sizing the treatment stage, Off Grid Water Treatment System: A Step-by-Step Guide to Sizing Yours (2026) is a useful companion.

  • Food-grade poly water storage tank: A sealed, UV-stabilized tank keeps stored water clean between refills. View on Amazon
  • Inline sediment filter housing: Protects the pump and fixtures from grit that settles or flows from the source. View on Amazon
  • Insect-proof tank vent: Keeps mosquitoes and debris out of the tank while allowing air to move in and out. View on Amazon

FAQ

How many days of water storage should an off-grid home have?

Three to five days is a practical minimum for a home with a dependable source such as a well. Rain-fed or seasonal sources need considerably more, often 30 days or greater, to cover dry spells.

Do I always need a pump with an off-grid water storage tank?

No. If the tank sits high enough above the fixtures, gravity can deliver adequate pressure with no electricity. A pump is needed when the tank is lower than the outlets or when you need higher pressure.

Is stored water safe to drink without treatment?

Not necessarily. Stored water can pick up bacteria, algae and sediment, so it should be tested and treated as needed. A licensed water professional or your local health department can advise on the right treatment for your source.

Conclusion

An off grid water storage system is built from three numbers: daily use, days of autonomy and the head and flow your pump or gravity line must deliver. Work those out first, then choose the tank, placement and protection that fit them. Keep the tank shaded, filtered and vented, and test the water regularly.

Ready to choose one?

Emily Parker

About Emily Parker

Emily Parker is part of our editorial team and reviews and edits our solar water systems guides, checking product details against manufacturer specifications and owner feedback.