Population Forecast Calculator
Population Forecast &
Water & Sewage Demand Calculator
A comprehensive tool for urban planners & civil engineers. Compute population projections, water demand, and sewage generation using all methods prescribed by the Central Public Health & Environmental Engineering Organisation.
Population Forecast
Enter census data for at least 3–4 decades. The calculator applies all CPHEEO-prescribed methods and recommends the most appropriate one based on growth trend analysis.
| # | Census Year | Population | Incremental Increase | % Growth Rate | Action |
|---|
Water Demand Calculator
Compute zone-wise water demand based on CPHEEO norms. Includes domestic, industrial, commercial, institutional, fire-fighting, and transmission losses.
Sewage Generation Calculator
Estimate sewage flow rates for sewer design based on CPHEEO standards. Includes domestic, trade/industrial effluent, infiltration, and storm contribution.
Method Comparison & CPHEEO Guide
Comparative analysis of all population forecasting methods prescribed by CPHEEO with applicability criteria and selection guide.
| Method | Best Suited For | Growth Pattern | Min. Data Needed | CPHEEO Recommended? |
|---|---|---|---|---|
| Arithmetic Progression | Old, stable, fully developed towns | Constant absolute increase | 2 census periods | ✓ Yes |
| Geometric Progression | New, fast-growing cities | Constant % increase | 2 census periods | ✓ Yes |
| Incremental Increase | Medium-growth towns | Variable — uses 2nd difference | 3 census periods | ✓ Yes — PREFERRED |
| Decreasing Rate of Growth | Saturating / crowded cities | Slowing growth rate | 3 census periods | ✓ Yes |
| Logistic (S-Curve) | Cities approaching saturation | S-shaped growth curve | 3 census periods + P_sat | ✓ Yes |
| Graphical Extension | Trend-based extrapolation | Visually extrapolated | 4+ census periods | ✓ Yes (visual check) |
| Comparative City Method | New towns / insufficient data | Based on similar city growth | 1 data point + comparator | ✓ If data scarce |
| City Class | Population | Domestic (LPCD) | Total Design (LPCD) | Peak Daily Factor |
|---|---|---|---|---|
| Metropolitan | >10 Lakh | 150–200 | 200–270 | 1.8 |
| Class I | 1–10 Lakh | 135 | 200 | 1.8 |
| Class II | 50K–1L | 110 | 150 | 1.8 |
| Class III | 20K–50K | 90 | 135 | 2.0 |
| Class IV | <20K | 70 | 100 | 2.0 |
| Rural Areas | Villages | 40–70 | 70 | 2.0 |
| Parameter | Value / Range | Remarks |
|---|---|---|
| Sewage as % of water supply | 70–80% | CPHEEO Standard |
| Minimum velocity in sewer | 0.6 m/s | Self-cleansing velocity |
| Maximum velocity | 3.0 m/s | Non-scouring limit |
| Minimum slope for 150mm sewer | 1 in 150 | CPHEEO |
| BOD of raw sewage | 200–300 mg/L | Typical Indian cities |
| BOD inlet at STP (Class I cities) | 250–300 mg/L | |
| BOD outlet standard (CPCB) | ≤ 30 mg/L | Discharge to water body |
| Harmon's Peak Factor range | 1.5–4.0 | For population 1K–1M |
Reference & Formulas
Complete formulas, CPHEEO references, and useful links for water supply and sanitation design.
Where: Ī = Average decadal increase = ΣΔP / number of decades
n = Number of decades to forecast
Assumes the population increases by a constant number each decade. Best for mature cities with slow, steady growth. Simple but may overestimate for slow-growing or underestimate for fast-growing towns.
r = Average geometric growth rate (%/decade)
log(P_n/P_0) / n → r computed per decade
Assumes constant percentage growth rate per decade. Suitable for fast-growing new towns. Tends to overestimate over long periods. CPHEEO advises caution for periods beyond 30 years.
Ī = Mean of incremental increases (1st difference)
r̄ = Mean of incremental changes of increments (2nd difference)
Most commonly recommended by CPHEEO. Accounts for acceleration or deceleration in growth. Requires minimum 3 census records. Balances between arithmetic and geometric methods.
x̄ = Mean decrease in growth rate per decade
Applied iteratively for each future decade
Used when the rate of growth is declining. Each decade gets a lower growth rate. Suitable for cities near their saturation population. Prevents overestimation common in geometric method.
P_sat = Saturation / carrying capacity population
a, b = Constants derived from past census data
t = Time from reference epoch (decades)
The most sophisticated CPHEEO method. Follows natural population growth — slow initially, accelerates, then slows as saturation approaches. Requires estimation of the saturation population. Pearl-Reed curve.
Data Sources
Standards & Guidelines
| IS Code | Title | Relevance |
|---|---|---|
| IS 1172 | Code of Basic Requirements for Water Supply, Drainage and Sanitation | Per capita norms |
| IS 4111 | Manual on Sewerage and Sewage Treatment | Sewer design |
| IS 10500 | Drinking Water Specification | Water quality |
| IS 1726 | Cast Iron Manhole Covers and Frames | Manholes |
| IS 783 | Laying of Concrete Pipes | Pipe laying |
| IS 2470 | Installation of Septic Tanks | On-site sanitation |
