1. Introduction

Urban residential colonies depend on a continuous, safe, and adequate supply of potable water to fulfil domestic, commercial, firefighting, and public utility requirements. In government-approved housing developments, the planning, design, and implementation of water supply systems must conform to the provisions of national building codes, public health engineering standards, and regulations issued by local governing bodies and development authorities. Compliance with these guidelines ensures public safety, system reliability, and

long-term sustainability. A scientifically designed water supply system involves several integrated components, including the identification and assessment of suitable water sources, transmission through conveyance systems, provision of adequate storage facilities, efficient distribution networks, and the incorporation of pumping arrangements where gravity flow is insufficient. Additionally, continuous monitoring and control of water quality are crucial to ensure that the supplied water meets the prescribed drinking water standards [1].

Components of a Water Supply Scheme

·         Water source (Groundwater / Municipal bulk supply/surface reservoir)

·         Intake well and Rising main

·         Treatment and disinfection (where applicable)

·         Overhead/underground storage reservoir (OHSR/UGR)

·         Distribution network (pipes, valves, hydrants)

·         Pumping system and control units

·         Household service connections and meters

2.       Population Forecasting

Population forecasting constitutes a critical foundation for the planning, design, and long-term sustainability of urban infrastructure systems, particularly municipal water supply networks. Reliable estimation of future population growth is essential to ensure that infrastructure capacity aligns with projected demand over the designated design horizon, thereby preventing both system inadequacy and inefficient overdesign. In the context of urban residential colonies, population projections are typically developed for a design period of 20–30 years and are derived from an integrated analysis of historical census data, prevailing demographic trends, migration patterns, land-use policies, housing density regulations, and socio-economic development indicators. These projections directly inform the estimation of domestic and non-domestic water demand, storage requirements, pumping capacities, and the dimensions of the distribution network. A range of established forecasting methodologies is employed depending on the stage of urban development and the reliability of available data. Conventional techniques, such as the arithmetic increase method, assume a uniform absolute growth rate and are generally applicable to mature or stabilised urban areas. The geometric increase method, which accounts for compound growth, is more appropriate for rapidly expanding urban settlements. The incremental increase method refines these approaches by incorporating variations in growth rates observed across successive decades. For planned residential developments and large urban agglomerations, advanced analytical models such as logistic growth curves and master plan based projections are often adopted to reflect growth saturation limits, regulatory constraints, and planned spatial expansion.

The selection of an appropriate forecasting approach is of paramount importance, as inaccuracies in population estimates can have significant technical and economic implications. Underestimation may lead to premature system failure, service deficits, and public health risks, while overestimation can result in unnecessary capital expenditure and suboptimal system performance. Consequently, population forecasting should be undertaken through a critical evaluation of multiple projection scenarios and validated against regional development strategies and policy frameworks.

Within water supply system design, population forecasts form the basis for determining per capita demand, peak demand factors, and fire-fighting water requirements. Thus, robust and defensible population projections are essential for the development of efficient, resilient, and sustainable urban water supply systems that can accommodate future growth and evolving demand patterns. The various methods of population forecasting are discussed below:

 2.1     Arithmetic Increase Method

For population projection, the arithmetic increase method is a straightforward and popular approach that works best in towns or urban regions with consistent and steady growth or slowly developing metropolitan regions because of its simplicity and ease of use.

                           (1)

where, = Population after n decades,  = Population at last known census,  = Arithmetic mean of population increases in the known decades, n = no. of decades.

2.2             Geometric Increase Method

A popular demographic strategy for predicting population growth, where the rate of increase is thought to be proportionate to the current population, is the geometric increase method.

This approach is easily suitable for metropolitan areas that are growing steadily and quickly as result of economic development, migration, and industrialisation. The geometric approach takes into account a consistent percentage growth over time, in contrast to the arithmetic increase method, which assumes a constant absolute rise. This approach projects the future population by first calculating the average percentage increase using the historical census data. The anticipated population  is calculated using the following expression after n decades:

                               (2)

where,  = Population at last known census, r = Assumed growth rate %,

Assumed growth rate % (r) is computed with

a. Arithmetic Average Method =   (3)

b.Geometric Increase Method

                              (4)

   2.3            Incremental Increase Method

The incremental increase method is a modified form of the arithmetic increase approach and is employed for population forecasting when historical data indicate a systematic variation in the rate of population growth. Unlike methods that assume uniform growth, this technique incorporates both the average decadal population increase and the average incremental change in that increase, thereby accounting for accelerating or decelerating growth trends over time. Consequently, it is particularly applicable to urban regions undergoing phased development, industrial expansion, or socio-economic transformation.

            The method involves determining the mean decadal population increase from past census records, followed by estimating the average incremental increase, defined as the mean difference between successive decadal increases. The projected population after  decades from the base year is computed using the following expression:

                              (5)
where, = Population after n decades,  = Population at last known census, n = no. of decades,  = Average Increase,  = Average Incremental Increase.

3.     Design Period

The design period is defined as the time span for which the components of a water supply system are planned to perform satisfactorily without requiring major augmentation. For a government-approved residential colony, the design period is selected based on statutory guidelines, expected population growth, functional life of infrastructure, and economic considerations.

As per the CPHEEO Manual on Water Supply and Treatment, the recommended design periods for various components of an urban water supply system are summarized in Table 1.

For the present study, a design period of 30 years has been adopted for population forecasting, source development, transmission mains, and distribution network, in accordance with CPHEEO recommendations. Mechanical components such as pumps and electromechanical equipment have been designed for a 15-year period, considering technological obsolescence and maintenance requirements. The treatment units have been planned with phased capacity augmentation to accommodate incremental demand over the design horizon.

Table 1 Components Design Period

Adopting a 30-year design period ensures long-term sustainability, optimal capital investment, and compliance with government norms for planned residential colonies.

Fig. 1 Flow chart of supply overview for 15-30 years.

4.            Estimation of Water Demand

Accurate estimation of water demand constitutes a fundamental component in the planning and design of urban water supply systems, as it directly influences the capacity of source development, treatment facilities, storage infrastructure, and distribution networks. For a government-approved residential colony, water demand assessment must conform to nationally accepted guidelines to ensure technical adequacy, operational reliability, and long-term sustainability[2].

In the present study, domestic water demand has been estimated in accordance with the CPHEEO Manual on Water Supply and Treatment, which recommends a per capita water supply of 135 litres per capita per day (lpcd) for urban residential areas equipped with piped water supply and sewerage systems. The average daily water demand has been computed as the product of the design population and the prescribed per capita demand.

In addition to domestic consumption, provisions have been incorporated for institutional, commercial, and public utility requirements, along with system losses, commonly referred to as unaccounted-for water (UFW). In line with CPHEEO recommendations, an allowance of 15–20% of the total demand has been considered to account for conveyance losses, leakage, unauthorized usage, and operational inefficiencies.

To capture temporal variations in consumption, appropriate demand factors have been applied. The maximum daily demand has been assumed as 1.8 times the average daily demand, while the peak hourly demand has been taken as 2.7 times the average daily demand. These demand multipliers are essential for the hydraulic design of pumping units, service reservoirs, and distribution pipelines to ensure satisfactory performance under peak load conditions.[3]

Accordingly, the design water demand has been determined by integrating average, maximum, and peak demand scenarios, thereby ensuring compliance with statutory norms and providing a resilient and efficient water supply system over the adopted design period.

4.1 Per Capita Demand

It is the annual average amount of daily water required by one person and includes the domestic, industrial and commercial use, public use, wastes, thefts etc.

                    (6)

4.2 Peak Demand Factor

The peak demand factor represents the ratio of the maximum short-term water consumption to the average daily demand and is used to account for temporal variations in water use within a distribution system. In accordance with the CPHEEO Manual on Water Supply and Treatment, the maximum daily demand is generally taken as 1.8 times the average daily demand, while the peak hourly demand is assumed to be 2.7 times the average daily demand. Accordingly, the peak demand factor ( ) may be expressed as:

                                            (7)

4.3 Fire Demand

Fire demand constitutes an essential component of total water requirement in urban water supply planning, particularly for government-approved residential colonies, where public safety and emergency preparedness are mandatory considerations. Fire demand represents the quantity of water required to control and extinguish fires and is generally characterized by short-duration, high-intensity withdrawal from the distribution system.

As recommended by the CPHEEO Manual on Water Supply and Treatment, fire demand is not directly added to the average daily water demand; instead, it is considered separately while designing the distribution network, storage reservoirs, and pumping capacity. The assessment of fire demand depends on population size, building density, land use pattern, and fire risk classification of the area.

For urban residential areas, fire demand is commonly estimated using empirical relationships such as Kuichling’s formula, which is expressed as:

                                                (8)
where = fire demand (litres per minute), = population of the area (in thousands)

5.     Storage Reservoir Capacity

Storage reservoirs play a critical role in urban water supply systems by balancing the temporal mismatch between continuous or intermittent water production and the fluctuating consumer demand. The capacity of storage reservoirs directly influences the reliability, operational flexibility, and pressure stability of the distribution network, particularly in government-approved residential colonies.

In accordance with the CPHEEO Manual on Water Supply and Treatment, the storage capacity is primarily designed to satisfy balancing storage requirements, fire demand, and emergency storage, depending on the system configuration and level of service. For systems with continuous pumping and supply, the balancing storage is typically considered to be one-third of the average daily demand. In cases where pumping is carried out for limited hours, additional storage is provided to compensate for non-pumping periods.

Fire storage is provided separately and is based on the estimated fire demand and the required duration of fire-fighting operations, typically ranging from 2 to 4 hours, depending on local fire safety regulations. Emergency storage is included to account for unforeseen events such as power failure, source interruption, or maintenance shutdowns and is commonly considered as 10–15% of the average daily demand. Thus, the total capacity of the storage reservoir ( ) may be expressed as:                                            (9)

Where, = balancing storage, = fire storage, = emergency storage

For the present study, the reservoir capacity has been determined by incorporating balancing, fire, and emergency storage components in compliance with CPHEEO recommendations. This approach ensures adequate system resilience, uninterrupted water supply during peak demand and emergency conditions, and conformity with statutory planning norms.

5.1. Balancing Storage

Balancing storage is provided in a water supply system to equalize the difference between the uniform rate of water production (treatment and pumping) and the non-uniform pattern of consumer demand over a 24-hour period. It ensures continuous and adequate supply during peak demand hours while maintaining operational efficiency.

As per the CPHEEO Manual on Water Supply and Treatment, for urban water supply systems operating with continuous pumping, the required balancing storage capacity is generally taken as a fraction of the average daily demand. The balancing storage ( ) may be expressed as:

                                      (10)

Where, = balancing storage capacity (m³), = average daily water demand (m³/day)

5.2. Balancing Storage

Fire storage refers to the portion of reservoir capacity reserved exclusively to meet water requirements during fire-fighting operations. Unlike balancing storage, fire storage is not associated with routine consumption but is provided to ensure adequate discharge and pressure for effective fire control, particularly in government-approved residential colonies where fire safety is a statutory requirement.[4]

In accordance with the CPHEEO Manual on Water Supply and Treatment, fire storage is determined based on the estimated fire demand and the duration for which the required flow must be sustained. The fire storage capacity ( ) is calculated using the following relationship:

                                          (11)

Where, = fire storage capacity (m³), = fire demand (m³/hour), = duration of fire-fighting operation (hours).

5.3. Emergency Storage

Emergency storage constitutes an essential component of reservoir capacity in urban water supply systems, providing continuity of supply during unforeseen disruptions such as power failures, mechanical breakdowns of pumping units, source contamination, pipeline damage, or scheduled maintenance activities. Unlike balancing and fire storage, emergency storage addresses system reliability and resilience in the event of abnormal operating conditions.

According to the CPHEEO Manual on Water Supply and Treatment, emergency storage is typically expressed as a fraction of the average daily water demand, ranging from 10–15% of the average daily demand, depending on the level of service, reliability of power supply, and operational characteristics of the system.

The emergency storage capacity ( ) may be expressed as:

                   (12)

Where, = emergency storage capacity (m³), = average daily water demand (m³/day)

Fig.1 Storage Reservoir Capacity

6.          Pipe Diameter and Distribution Design

The design of pipe diameters and the layout of the distribution network are critical aspects of urban water supply systems, as they directly influence hydraulic performance, service pressure, water quality, and overall system reliability. For a government-approved residential colony, the distribution system must be designed to deliver the required quantity of water at adequate pressure under peak demand and fire-flow conditions, in compliance with statutory standards.

In the present study, pipe diameters have been determined based on the peak hourly demand, incorporating the adopted peak demand factor, to ensure satisfactory performance during periods of maximum consumption. Hydraulic design has been carried out using the continuity and energy equations, with head losses estimated using the Hazen–Williams formula, as recommended by CPHEEO for water distribution systems:

                                        (13)

Where, = head loss due to friction (m), = length of pipe (m), = discharge (m³/s), = internal diameter of pipe (m), = Hazen–Williams roughness coefficient

The value of the roughness coefficient ( ) has been selected based on the pipe material, typically ranging from 110 to 140 for commonly used materials such as ductile iron and PVC.

The distribution network has been designed as a looped (grid) system, which offers superior hydraulic performance, improved pressure balance, and enhanced reliability compared to dead-end systems. Minimum residual pressure of 7–12 m at consumer taps has been ensured under peak demand conditions, in accordance with CPHEEO recommendations. Additionally, pipe velocities have been maintained within the desirable range of 0.6 to 2.0 m/s to prevent sediment deposition and excessive head losses.

Fire-flow requirements have been superimposed on the peak demand scenario to verify the adequacy of pipe diameters and network configuration under emergency conditions. The final pipe sizes have been selected by satisfying hydraulic constraints related to discharge capacity, allowable head loss, velocity limits, and minimum pressure criteria.

Thus, the adopted pipe diameter selection and distribution network design ensure efficient, reliable, and standards-compliant water supply throughout the service area over the design period.

Case Study:

Present population, = 4,000 persons

Design period, = 20 years

Annual growth rate, = 2% = 0.02

Per capita water demand, = 135 lpcp

Peak demand factor, = 2.0

Design Population Estimation

(Using Geometric Increase Method, commonly adopted for urban planning)

2. Average Daily Water Demand

3. Peak Water Demand

4. Peak Discharge (for Distribution Design)

Maximum Daily Demand

Required Storage (30% of daily demand)

Example Pipe Flow Calculation

Assume demand through main = 20 L/s, velocity = 1.0 m/s

Design Considerations and Standards for Water Supply Scheme in a Government Residential Colony

The water supply scheme for a government residential colony shall be planned and designed to provide a continuous, safe, and adequate supply of potable water in accordance with CPHEEO Manual on Water Supply and Treatment, relevant BIS standards, and applicable state Public Health Engineering Department (PHED) guidelines. The system shall be designed to meet present and future demands over the approved design period with due consideration to operational efficiency, public health safety, and sustainability.

Design Period

The design period shall be selected based on projected population growth, service life of components, and scope for future expansion. As per CPHEEO guidelines:

Distribution system: 30 years

Service reservoirs (OHT/UGR): 30 years

Pumping machinery and electromechanical equipment: 15 years

Population Forecasting

The future population of the government colony shall be estimated using standard forecasting techniques such as the geometric increase method or incremental increase method, depending on historical growth trends and approved housing plans. The projected population at the end of the design period shall form the basis for demand estimation.

Water Demand Norms

Per capita water demand shall be adopted as per CPHEEO norms:

Residential demand (with sewerage): 135 lpcd

Floating population and public uses: 5–10% of domestic demand

Unaccounted-for water (UFW): 10–15%

Fire demand shall be assessed separately in accordance with IS 9668 or local fire authority requirements.

Demand Variations and Peak Factors

To account for temporal variations in water use:

Maximum daily demand = 1.8 × average daily demand

Peak hourly demand = 2.0 – 3.0 × average hourly demand
The system shall be hydraulically adequate to meet peak-hour demand conditions.

Source of Water Supply

The source shall be selected based on adequacy, reliability, quality, and sustainability. Surface water, groundwater, or a conjunctive source may be adopted. The raw water quality shall conform to IS 10500: Drinking Water Specifications after treatment.

Treatment and Disinfection

Water treatment facilities, if required, shall be designed based on source water quality. Minimum treatment shall include filtration and disinfection. Chlorination shall be provided to maintain a residual chlorine level of 0.2–0.5 mg/L at consumer ends.

Distribution System Design

·         The distribution network shall be designed to ensure:

·         Minimum residual pressure of 7 m at the farthest consumer point during peak demand

·         Minimum velocity of 0.6 m/s for self-cleansing

·         Maximum velocity not exceeding 2.5 m/s
Hydraulic design may be carried out using the Hazen–Williams equation, ensuring economical pipe diameters.

Pipe Materials and Standards

·         Pipe materials shall be selected based on durability, soil conditions, pressure requirements, and lifecycle cost. Commonly adopted materials include:

·         Ductile Iron (DI) pipes conforming to IS 8329

·         HDPE pipes conforming to IS 4984
All fittings, valves, and appurtenances shall conform to relevant BIS standards.

Storage and Pumping Facilities

·         Underground reservoirs and overhead service reservoirs shall be designed to meet:

·         Balancing storage

·         Fire demand

·         Emergency storage Pumping systems shall be designed for peak demand with 100% standby capacity to ensure an uninterrupted water supply.

Firefighting Provision

Fire demand shall be incorporated as per IS 9668 and local fire department norms. Fire hydrants shall be strategically located within the colony to ensure accessibility and safety.

Operation, Maintenance, and Reliability

The system shall be designed for ease of operation and maintenance. Isolation valves, bulk meters, and pressure-reducing valves shall be provided to ensure effective system control and minimise water losses.

Sustainability Considerations

Water conservation measures such as rainwater harvesting, leakage control, and energy-efficient pumping shall be integrated into the design. The scheme shall support long-term sustainability and resource optimisation.[5]

This study presents a comprehensive and standards-based methodology for planning and designing water supply systems for government-approved residential colonies. By integrating population forecasting, water demand assessment, storage reservoir sizing, pumping requirements, and hydraulic design of the distribution network, the proposed approach ensures technical adequacy, operational reliability, and regulatory compliance over the designated design period. Adoption of CPHEEO guidelines, relevant BIS standards, and statutory norms provides a robust framework for delivering safe and adequate potable water while accommodating future population growth.[6]

The case study demonstrates the practical applicability of the methodology and highlights the importance of accurate population projections and demand estimations in achieving an efficient and cost-effective system design. Proper consideration of peak demand variations, fire-fighting requirements, and emergency storage enhances system resilience and public safety. Furthermore, the use of looped distribution networks, appropriate pipe sizing, and controlled velocities ensures satisfactory hydraulic performance and long-term serviceability.

Overall, the findings affirm that a systematic, scientifically grounded, and regulation-compliant design approach is essential for sustainable urban water supply planning. The methodology outlined in this paper can serve as a reference framework for engineers, planners, and policymakers involved in developing residential water supply infrastructure, and it can be effectively adapted to similar urban settings with varying scales and growth characteristics.[7]

6. Conclusion

The case study clearly demonstrates that effective safety practices are essential for multi‑storied building construction projects. Proper planning, training, PPE usage, and continuous monitoring can significantly reduce accidents. Numerical safety indicators such as AFR and ASR are useful tools for evaluating safety performance. Ensuring a safe working environment not only protects workers but also enhances project efficiency and quality.