When to use this calculator
Estimate how long usable stored water lasts at a fixed daily withdrawal. Assumes no replenishment, leakage or change in demand; does not assess water potability.
Explore the water use & conservation calculators for other questions in this topic. For a related calculation, use the Water Bill Calculator: Estimate water charges from a volume-based rate and a fixed period charge.
PUTTING IT INTO PRACTICE
Stored Water Supply Days: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Usable stored water (litres) | 1,000 |
| Daily withdrawal (litres) | 100 |
| Result | 10 days |
- Check the input labels and enter the example values above.
- Apply the relationship: Supply duration = usable storage/daily withdrawal.
- The result is 10 days, rounded for display.
How to interpret your result
Assumes no replenishment, leakage or change in demand; does not assess water potability.
Use measured flow rates when possible. A rainfall volume estimate is not a storage simulation and can exceed tank capacity. Fixed water charges and sewerage charges may follow separate tariff rules.
Frequently asked questions
Can rain collected exceed tank capacity?
The geometric collection estimate can. Storage, overflow, first-flush diversion and use during rainfall need a separate tank model.
When is the stored water supply days calculator useful?
Estimate how long usable stored water lasts at a fixed daily withdrawal. Assumes no replenishment, leakage or change in demand; does not assess water potability.
How do I use the stored water supply days calculator?
Enter usable stored water (litres), daily withdrawal (litres). The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Supply duration = usable storage/daily withdrawal.
What should I check before using the result?
Assumes no replenishment, leakage or change in demand; does not assess water potability.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
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