CHAPTER 1

Introduction and Design Considerations

Introduction & Design

Defines the objective of urban water supply systems — quantity, quality, continuity, pressure, and cost — and establishes the framework for design period, design population, service levels, per capita supply, and reliability. Sets the governing principles that subsequent chapters operationalize.

📋 Planning & Design PeriodManual on Water Supply and Treatment3rd Edition (1999) with 2024 revision updates

Key values & thresholds

design period source works years: 30
design period pumping machinery years: 15
design period treatment plant years: 15
design period distribution mains years: 30
design period service reservoirs years: 15
service level urban lpcd: 135 (piped + sewered)
service level urban no sewer lpcd: 70
service level rural lpcd: 55 (BIS 2012) / 40 (CPHEEO legacy)
continuity target hrs per day: 24 (per JJM/AMRUT goal)

Clause-level requirements

Design period for civil structures (reservoirs, transmission mains, treatment works, civil buildings) is 30 years from year of commissioning.
Design period for pumping machinery, treatment plant equipment, and service reservoirs with mechanical components is 15 years.
Intermediate pumping/boosting equipment is designed for 15-year horizon due to technology obsolescence and wear.
Three service-level scenarios defined: (a) piped water + underground sewerage 135 lpcd, (b) piped water without sewerage 70 lpcd, (c) stand-post water supply 40 lpcd.
Reliability criteria: source yield ≥ peak day demand; distribution system operable at 50% load with one pump standby; redundancy essential at all critical links.

Practitioner notes — what goes wrong in the field

Design period 30 years for civil mains is a conservative assumption — many older systems (Mumbai, Delhi, Chennai) have mains > 80 years old still in service, but at reduced capacity.
15-year horizon for pumping machinery is realistic — major pump overhauls are expected every 7-10 years; full replacement every 15-20.
For Jal Jeevan Mission (JJM) rural schemes: design for 55 lpcd per BIS 1172:2012 (up from older 40 lpcd CPHEEO value). Coverage 100% FHTC (Functional Household Tap Connections) by 2024.
AMRUT Mission urban: 135 lpcd with 24×7 pressurized supply. Existing intermittent supply (2-6 hrs/day) being converted to 24×7 in phases.
Design population: use highest of (a) geometric growth, (b) incremental growth, or (c) logistic curve — whichever gives largest forecast. Reassess every 10 years.
Peak factor hierarchy: source intake × 1.0; raw water transmission × 1.0; treatment plant × 1.1; clear water pumping × 1.5; distribution × 2.5-3.0.
Service levels in Indian cities widely inconsistent — Delhi varies from 40 to 280 lpcd by zone; average urban India 125-135 lpcd actual consumption.

FAQs

What is the standard design period for water supply?

Per CPHEEO Chapter 1: civil structures (pipelines, reservoirs, treatment plant buildings) 30 years; pumping machinery, equipment, mechanical components 15 years. These account for asset longevity and technology obsolescence.

What is LPCD and what are the CPHEEO values?

LPCD = Litres Per Capita per Day — average daily water supply per person. CPHEEO values: 135 lpcd for urban with sewerage; 70 lpcd urban without sewerage; 40 lpcd rural (legacy) or 55 lpcd per BIS 1172:2012 (JJM current).

How is design population calculated?

Use the highest forecast from (a) geometric growth (for rapidly growing cities), (b) incremental growth (steady growth), or (c) logistic curve (S-curve for cities approaching saturation). Forecast to design horizon (30 years) and reassess every 10.

Cross-references

IS 1172CPHEEO Sewerage ManualAMRUT 2.0Jal Jeevan Mission