Low-yield well storage worksheet
Test one documented event against the usable water already in an intermediate reservoir and a deliberately chosen refill condition. The worksheet also keeps the full-day supply balance visible.
Developed with AI assistance; not reviewed by a licensed well or pump professional. Educational fixed arithmetic only. No individual professional or AI assessment occurs. Method and sources · Conditions of use
Your event worksheet
Enter the documented values and confirm both conditions.
Display rounding makes the arithmetic readable; it is not measurement precision.
- Chosen daily demand
- US gal/day
- Documented daily supply volume
- Daily balance
- Event volume and time
- Average event demand rate
- US GPM
- Refill credited during event
- Event drawdown after credited refill
- US gal
- Usable capacity / water at start
- Event shortfall
- Usable water at end
- US gal
- Potential unretained inflow at capacity
- US gal
- Penn State full-day storage reference
- US gal
This is one uniform-demand volume balance, not a tank size, supply guarantee, overflow prediction, or equipment recommendation. Actual control logic may stop refill; changing demand, pressure, pump delivery, seasonal yield, reserve needs, repeated events, sanitation, code, and usable-level settings require separate evidence and design.
Developed with AI assistance; no licensed professional review. Confirm measurements, controls, current source requirements, and system design with an appropriately qualified professional.
Method storage-1.0.0 · Sources checked September 8, 2026 Toronto.
Penn State Extension, “Using Low-Yielding Wells,” updated September 8, 2025: Intermediate Storage and Storage Tank Capacity · Penn State Extension, “Water System Planning: Estimating Water Needs,” updated May 29, 2025: peak-demand planning
Method, terms, assumptions and sources
Sustainable well yield is a rate that can be maintained without lowering water below the pump intake. Installed pump delivery is the rate the installed system can transfer under actual conditions. The worksheet’s fill rate cannot exceed either one. Wellbore storage is water standing in the well and may become unavailable as water levels change. Pressure-tank drawdown is usable delivery between pressure-switch limits and is smaller than nominal capacity. Intermediate usable water is the water available in a nonpressurized reservoir between operating limits; only this last quantity belongs in capacity and start.
Daily demand is people × chosen allowance + additional demand. With known pumping hours, daily supply is usable rate × 60 × hours, and daily balance is supply minus demand. Unknown hours keep both daily supply and balance explicitly unknown.
For the confirmed uniform event, continuous inflow is usable rate × event minutes; no refill is zero. Drawdown is the larger of zero and event volume minus inflow. Shortfall is the larger of zero and event volume minus inflow minus usable water at start. Ending usable water is the unconstrained end clamped between zero and usable capacity. Potential unretained inflow is any unconstrained end above capacity; it is arithmetic for a capacity limit, not a claim that a real system overflows because controls may stop refill.
Penn State separately gives a 100-US-gallons-per-resident rule of thumb for storage intended to hold a full day’s use and says enough for a two-hour peak is a minimum planning concept. This worksheet shows the full-day reference separately. It does not add a buffer, round to catalog tanks, recommend a refill time, or prove next-day recovery.
New York State Department of Health Fact Sheet #2, “Individual Water Supply Wells — Water Storage” (revised July 2024, Well Yield, Water Demand, and Storage; Steps in Determining Supplemental Storage Needs; Storage Recommendations), offers a jurisdiction-specific bedroom/yield table for typical moderate-use residences. It is not blended into this formula and may not apply outside New York or to higher-use homes. Read the New York guidance.
Product bounds are 1–20 people, 1–250 US gal/person/day, 0–5,000 additional US gal/day, 0–100 US GPM, 0–24 hours/day or unknown, event volume over 0 through 10,000 US gal, duration over 0 through 1,440 minutes, usable capacity over 0 through 20,000 US gal, and event-start water from 0 through capacity. These are worksheet limits, not engineering standards.
Teaching example: four people × 100 US gal/person/day, no additional demand, a documented 1 US GPM rate available 16 hours/day, a 300-US-gallon event over 120 minutes with continuous refill, 400 US gallons usable capacity, and 200 US gallons at the start. Event inflow is 120 US gal, drawdown is 180, shortfall is zero, and 20 remain. Daily supply is 960 US gal against 400 US gal demand.
Primary sources: Penn State Extension, “Using Low-Yielding Wells” (updated September 8, 2025; What Is Well Yield, Peak Demand, Pressure Tank Storage, Intermediate Storage, Storage Tank Capacity, Well Pump Capacity, Borehole Storage) and Penn State Extension, “Water System Planning: Estimating Water Needs” (updated May 29, 2025; Estimating Home Water Use Needs and peak-demand planning). Sources checked September 8, 2026 Toronto; WDG method storage-1.0.0.