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Water & property
Water tank capacity and usable reserve
A 2,500-gallon tank does not necessarily contain 2,500 gallons, and the water currently in it is not all necessarily available for your next planned use.
Give each quantity a separate name
Capacity describes the tank’s nominal storage size. Stored volume describes the water currently inside. A planning reserve is an amount you choose to hold back. Water above that reserve is a calculation based on the stored volume and reserve.
Keep physically inaccessible water separate too. Outlet position, tank shape and the delivery arrangement can affect how much is usable. A dashboard subtraction cannot establish those details or determine whether the water is suitable for a particular use.
Work through the arithmetic
An illustrative tank
Capacity: 2,500 gal. Assumed stored volume: 1,800 gal. Planning reserve: 500 gal. Water above reserve is 1,800 − 500 = 1,300 gal. Stored volume is 72% of nominal capacity.
At an assumed draw of 100 gal/day with no refill, the simple estimate is 13 days to reserve. At 200 gal/day, it is 6.5 days. Neither result predicts actual household demand or confirms that all modeled water can be delivered.
At or below the reserve, report zero above-reserve water rather than a negative usable quantity. If daily draw is zero or unknown, a meaningful time-to-reserve estimate is unavailable.
Do not turn height into gallons without geometry
A level sensor may report distance or depth. Converting it into volume needs the tank’s shape and dimensions or a suitable calibration chart. Half the measured height is not always half the volume, especially in a horizontally oriented curved tank.
Keep the raw measurement and conversion method in the installation record. If the sensor mounting height changes, the old calibration may no longer describe the installation. A precise-looking gallon count can still depend on uncertain geometry.
Keep water quality outside the level calculation
Volume is not evidence of drinking-water safety. Contamination, treatment and local advisories are separate questions. The CDC’s cistern guidance addresses disaster-related contamination concerns; a full tank can still require a different response from a low but suitable supply.
Use appropriate professional and public-health guidance for the actual water system. Do not infer quality from a level chart or use a reserve percentage as a substitute for an emergency drinking-water plan.
Understand Sunstead’s current water preview
Sunstead’s water view currently uses illustrative level, daily-use and reserve values. The 2,500-gallon example and 500-gallon demo reserve are preview assumptions, not a recommended reserve for every property. No tank sensor is connected through this preview, and it does not control a pump.
- Label every input as measured, rated or assumed.
- Record the tank geometry and usable outlet range.
- Choose a reserve for the property’s actual needs.
- Include refill assumptions explicitly.
- Keep sensor integration and water quality as separate checks.
Use the preview to understand the calculation, then require real measurements and an implemented data path before treating a future dashboard as an operating instrument.
Sources & further reading
Documentation checked October 10, 2026.
Your next step
Plan the sensor data path