Choosing a water supply for an off-grid home

Compare complete supplies, not just sources

For each option, sketch the path from source to tap: collection or extraction, transport, storage, treatment, pumping and distribution. Put the power requirements and maintenance beside that sketch. A cheap source with a costly delivery route or difficult treatment need may be a poor fit for the household.

Take the proposed source to the dwelling approval office before buying tanks or commissioning a well. Ask what evidence it accepts and which other agency governs extraction, collection or treatment. The calculations below are planning exercises; they do not establish a water right or an approved drinking-water system.

Build a water budget from your household

Separate indoor demand from irrigation, livestock, workshop use and any dedicated fire-water requirement. Estimate each from measurements or equipment information where possible. For a move from a connected house, recent meter records are a starting point, but separate outdoor use and leaks before transferring the figure to a different property.

Make both a normal-day budget and a demanding-day budget. Visitors, laundry, cleaning treatment equipment and simultaneous use can change the peak. Ask the system designer how much storage is actually usable and whether reserves, tank outlets or operating controls restrict it.

Worked example: storage is time, not a new source

Assumptions for arithmetic only: two people use 40 gallons each per day indoors, plus 10 gallons per day for other planned uses. Total demand is 90 gallons per day. This is not a recommended allowance or a permit design flow; measure and design for your own use.

If a tank has 1,800 gallons of usable water available for those uses, it represents 1,800 ÷ 90 = 20 days without replenishment. A 500-gallon reserve reduces the available amount to 1,300 gallons, or about 14.4 days. Any legally or operationally required reserve must remain separate from ordinary consumption.

The useful question for a hauled supply is therefore not simply whether a truck can fill the tank. It is when to order, what delivery delay the remaining usable water can cover, and whether the refill quantity fits the available capacity. Get those numbers before agreeing to a delivery schedule.

Test rainwater against dry periods

The Texas Water Development Board’s rainwater FAQ gives a theoretical collection factor of approximately 0.62 gallons per square foot of roof per inch of rain. Actual capture is reduced by losses. That physical estimate is useful elsewhere; Texas’s legal discussion is not a national rule.

Illustrative calculation: a 1,000-square-foot catchment receiving 1 inch of rain, with an assumed 80% collection efficiency, captures about 1,000 × 1 × 0.62 × 0.80 = 496 gallons. At the example household’s 90 gallons per day, that event supplies about 5.5 days. The 80% efficiency is a teaching assumption, not a specification for your roof.

Annual rainfall hides the timing problem. Make a monthly water balance that carries stored water forward, caps storage at tank capacity, accounts for overflow and shows any deficit. Then stress-test longer dry sequences with an appropriate local rainfall record. Monthly arithmetic itself can still hide several dry weeks within a wet month; a designer may need a finer time step.

Download the monthly water-balance worksheet. It provides columns, not a finished system model. Keep units consistent and document the catchment, losses, usable capacity and demand used. A tank that begins the model full should have an identified source for that first fill.

Read well records as different kinds of evidence

A construction record, pumping test and water-quality result answer different questions. Ask the well professional to explain the well’s construction, the test duration and conditions, what was measured, and what can reasonably be inferred about ongoing supply. Ask how storage and pumping would accommodate the household’s peak use.

For an existing well, match the record to the actual well on the parcel. Obtain pump details, service history and any changes to treatment. For a new one, use neighboring records to frame questions and a drilling budget—not as a guarantee of depth, yield or chemistry at your site. Request separate scope for an unsuccessful bore or a source needing additional treatment.

EPA recommends annual private-well testing for total coliform bacteria, nitrates, total dissolved solids and pH, with additional tests based on local conditions. Its guidance also identifies events such as repairs, flooding or changed water quality that warrant testing. Use a laboratory certified for drinking-water testing and ask the local health department which additional contaminants matter at the property.

A laboratory result only reports what was sampled and tested at that time. Keep the sampling location, treatment status and date with it. If treatment is proposed, ask what it is intended to remove, what it cannot address, how performance is checked and where its waste or backwash goes. Do not choose equipment from taste or appearance alone.

Make the backup and maintenance plan specific

A backup that uses the same failed pump, inaccessible road or unpowered controls may not solve the actual problem. Walk through three situations: source interruption, equipment interruption and a water-quality problem. Identify the person to call, the alternative supply, the storage available and the conditions for returning to normal service.

Budget for testing, filters or other consumables, pump energy, delivery charges, maintenance access and eventual equipment replacement. Keep the well and wastewater layouts coordinated: changes to one may constrain the other. Bring the final operating assumptions to your electricity load list and property budget.

To continue with jurisdiction-specific evidence, see Arizona’s water-source guide, Colorado’s water and property questions or your own state guide. Each explains its own source dates and scope.

Before putting the water system into service

Ask the installer for a startup and handover plan covering the source, storage, treatment and plumbing as a complete supply. Name who will arrange any required sampling, which laboratory will analyse it, and what evidence the approval office needs. Keep the sampling point, treatment status and date with the results.

Have the installer explain the normal operating range, controls, pump protection, treatment servicing and the response to loss of supply or a quality concern. Record model numbers, installed settings, consumables and the local service contact. Ask which checks need repeating after work on the system; use the linked EPA well guidance and local requirements for the actual sampling plan.

Include the final layout, source records and equipment manuals in the handover worksheet. A delivery receipt for tanks or filters is only one part of this record. Arrange the next service or review date and make the operating instructions available to everyone responsible for the home.