Plan sewer capacity with clear peak estimates. Choose Harmon, fixed, or custom peaking methods instantly. Download CSV or PDF, then share results with teams.
| Scenario | Population | Per-Capita | I/I | Method | Safety | Design Peak |
|---|---|---|---|---|---|---|
| Small township | 5,000 | 180 L/p/d | 1.0 L/s | Harmon | 10% | ~7.2 L/s |
| Mixed-use district | 20,000 | 160 L/p/d | 3.0 L/s | Fixed PF=2.5 | 15% | ~18.8 L/s |
| Large service area | 120,000 | 150 L/p/d | 10.0 L/s | Custom PF=2.0 | 10% | ~68.3 L/s |
Peak sanitary flow depends on population, per‑capita use, and allowances added for nonresidential demand. For preliminary sizing, 120–250 L/person/day is common; higher values may apply where water use is elevated. Separating domestic average flow from other average flow keeps assumptions transparent during review. Cross‑check per‑capita values against local billing data when possible.
Short‑term demand variation is represented by a peaking factor (PF). The Harmon option adjusts PF with population size, typically producing higher PF for smaller communities and lower PF for larger systems. Fixed or custom PF can match local standards, calibrated diurnal curves, or meter‑based studies. Very high PF values can oversize pipes and reduce cleansing velocity.
Infiltration/inflow (I/I) is entered as L/s or L/day and is added to both average and peak results. Use measured wet‑weather response where available, or apply a conservative allowance for aging pipe networks, high groundwater, or poor joints. Document assumptions and update I/I as rehabilitation programs improve performance. Where criteria separate base infiltration and inflow, record both components.
The calculator first converts daily volumes to L/s, then applies PF to sanitary flow excluding I/I. Next, it adds I/I and applies a safety factor to produce a design peak. Report conversions to m³/s, gpm, and MGD support coordination between hydraulic modeling, pipe sizing, and pump station checks. Apply 5–20% safety depending on growth horizon and data quality.
Use the example table to sanity‑check magnitudes before committing to pipe diameters. If the resulting design peak seems low, verify units and confirm that other average flow is entered as L/day, not L/s. Export the CSV for design notes and the PDF for submittals, keeping method, PF, and safety factor visible. Save exports with project ID and date for traceable updates. If downstream capacity is limited, run sensitivity cases with higher I/I and PF, then coordinate required storage, upsizing, or rehabilitation before final approval.
Peak sanitary flow supports sewer pipe sizing, pump station checks, and hydraulic modeling. It represents short-duration maximum demand plus allowances such as infiltration/inflow and design safety margins.
Diurnal peaking mainly affects sanitary discharge from users. Many criteria treat I/I as a separate allowance added to the peak because it is not driven by hourly user behavior.
Use Harmon when you need a population-based PF and local standards accept it. Use fixed or custom PF when your authority specifies a constant value or you have monitored diurnal patterns.
Prefer measured wet-weather flow monitoring or calibrated model results. If unavailable, use agency guidance and consider pipe age, groundwater level, and known defect rates. Update the allowance as rehabilitation reduces I/I.
Many designs use 5–20% depending on growth horizon and uncertainty. Use higher values where land use is changing rapidly or downstream constraints require extra capacity.
Use L/s when criteria provide a direct hydraulic allowance or when translating wet-weather monitoring peaks. Use L/day when you have average daily I/I volumes and want consistent daily accounting.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.