Separate four demand questions
| Question | Useful quantity | Why it matters |
|---|---|---|
| How much over a day? | Average daily volume | Source production and operating schedule |
| How fast at the busiest time? | Peak flow | Pump, pipe and pressure duty |
| How long does the peak last? | Peak duration | Short-term storage gap |
| How long must service continue? | Outage / autonomy period | Bulk usable storage |
Demand inventory
List occupants or process units, indoor essential uses, discretionary uses, irrigation, livestock or production needs, seasonal variation, losses and any treatment reject or backwash. Use measured records where available and keep unusually high days visible rather than averaging them away.
Refill and source factors
Record sustained source rate, available pumping or refill hours, seasonal low conditions, maintenance downtime and the probability that refill remains available during the planned outage. A source rating multiplied by 24 hours is not a defensible daily supply unless continuous operation is actually available.
Reserve and safety margin
State the reason for any margin: uncertain demand, uncertain refill, inaccessible volume or an operational policy. Do not mix fire storage, mandated emergency volume or water-quality turnover into an unexplained percentage.
Scenario worksheet
| Scenario | Demand | Source / refill | Storage question |
|---|---|---|---|
| Typical day | Measured average plus known uses | Normal sustainable availability | Turnover and normal cycling |
| Peak period | Peak rate × duration | Source contribution during peak | Peak gap and delivery rate |
| Outage | Essential daily demand × days | None or credible partial refill | Usable volume plus stated reserve |
| Dry / stressed case | Seasonal demand | Reduced well yield or rainfall | Reliability and contingency |
Sources
- U.S. EPA — Emergency Drinking Water Supply Guidance
- U.S. CDC — Cistern Safety and Disasters
- U.S. Geological Survey — Basic Ground-Water Hydrology