Design of water distribution / supply systems

VEHA - Field Implementation Guidance

Welcome

Water supply, Sanitation and Hygiene Promotion (WASH)

Access to water for human consumption

Water distribution

Design of water distribution / supply systems

Context

Overview

Environmental factors causing/contributing to the needs and affecting the humanitarian activity

Water distribution/supply systems can reduce environmental impacts, for example by reducing the amount of domestic boiling of water using firewood or fossil fuels.

However water distribution networks also create environmental impacts including potential damage to water courses, drainage, and ecosystems in their construction and maintenance; the manufacture and use of chlorine to dose the water; leakages causing soil erosion, local habitat destruction, and water loss; the ingress and multiplication of bacteria and other contaminants hazardous to health; and the burning of fossil fuels for energy for pumping; and water wastage due to lack of flow control devices and wasteful end-user behaviors.

Inappropriate pricing mechanisms can also prevent the poor and ultra-poor from accessing clean water, which can lead to them being forced into more harmful water abstraction coping mechanisms.

Implications

Gender, age, disability and HIV/AIDS implications

People with disabilities, the very young, very old, and people with disabilities or long term health conditions or terminal illness are in greater need of water being piped to their homes than more healthy or able-bodied people.

Women usually take on the greater burden of both fetching and using water. Their water needs should be assessed and support given to them to understand how to conserve water. They should be supported with the provision of flow control devices.

Women, the disabled, the sick, the elderly, and children are usually the least able to pay for water. Water should be priced to ensure that all people can access their minimum basic daily requirement, and use above that can be charged for at higher rates.

Impacts

Environmental impact categories

Soil pollution
Water pollution
Loss of biodiversity and ecosystems
Natural Resource depletion
Soil erosion

Summary of Impacts

Summary of potential environmental impacts

Soil erosion due to leakages in water distribution systems.

Water wastage/depletion due to lack of low flow control devices.

Inappropriate design of water supply systems and poorly structured water pricing mechanisms results in environmentally damaging water collection coping methods, resulting in soil erosion and water depletion.

Impact detail

Detailed potential environmental impact information

Poorly designed piped networks can break and leak and require increased levels and complexity of maintenance. Leakages cause soil scouring and erosion and water wastage and pollution. Improperly constructed or maintained or operating systems are vulnerable to pipe breakages.

When water supply flow rates are not restricted the amount of water used per second is higher than when low flow devices are installed. If those devices are not available, water consumption per capita may be high to the point where available water resources start to deplete.

Improper design of water supply systems that do not accommodate community cultural practices and inappropriately tiered water pricing mechanisms, may force the community into environmentally damaging water collection approaches. This can have negative impacts on natural resources.

Guidance

Summary

Summary of environmental activities

Design and maintain water distribution systems using high-quality materials, good quality network modeling software to avoid creating air blocks or vibration stress fractures.

Design and install low or efficient flow devices in the system

Understand the perception, needs, and cultural practices of affected people, and their ability to pay for water

Detail

Detailed guidance for implementing suggested environmental activities

The use of proper water distribution network modeling software, and the installation of air valves, stop cocks, and where feasible, radial/ring systems, reduces the frequency of pipe breakages and makes maintenance, cleaning, and network extensions easier.

A piped water network handover strategy should include training for the operator(s) and a strategy to finance future maintenance and operational costs.

A maintenance plan should be devised with the service provider or operator, with strategies in place to ensure compliance with the plan.

Map potential sources of pollution to ensure that water flowing through leaky systems is tested in case of pollution by pollutants in the environment through which pipes pass.

Installing low or efficient flow devices should be planned for in order to preserve and control the number of water people use.

When designing water supply systems, investigate and understand the cultural practices related to the water usage of the affected people in order to properly design water supply systems that allow for proper and continued usage. This should reduce possible environmental damage from alternative water extraction actions. The system should be appropriately designed to meet the preferences of the end users, because overlooking user preferences can lead to a lack of usage or inappropriate behavior by users that can result in negative impacts on the environment.

Developed tiered tariffs for different user types to ensure the poor and ultra-poor can access safe clean water.

Lessons Learnt

Lessons from past experiences

Controlling water losses through leaks in water supply systems is of great importance for the sustainable management of this scarce resource in South Africa and the world.

Much work has been done in this field, both locally and internationally, and various factors influencing water losses have been identified and investigated. One of the major factors still not well understood, is the effect of the water pressure in a pipe on the leakage rate.

According to the theory, the rate of leakage through a hole in a pipe is proportional to the square root of the pressure. However, using measurements in real water distribution systems, especially in the UK and South Africa, it has been found that pressure has a much greater effect on the leakage rate than the theory predicts. To illustrate this point, doubling the pressure in a pipeline will increase the theoretical rate of leakage by approximately 40 %. However, in practice the real increase in the rate of leakage is typically 100 %, and increases as high as 570 % have been reported. Various possible reasons for the discrepancies between the theory and practice exist. The purpose of this paper is to identify the main mechanisms that may be responsible for these discrepancies. The mechanisms discussed include expanding leak openings, the effect of soil conditions around the pipe, and laminar flow conditions.

The importance of water conservation and water loss reduction should always be an integral part of the management of freshwater resources and needs to be given prominence in freshwater resources planning. For water management purposes, the community can be divided into two basic groups: system users (such as households, industry, and agriculture) and system operators (such as municipal, state, and local governments and privately owned suppliers). These users have a choice of a number of different practices, which promote or enhance the efficiency of their use. These practices fall into two basic categories: engineering practices, based on modifications to hardware (e.g., plumbing and fixtures) and/or water supply operational procedures, and behavioral practices, based on changing water use habits.

Engineering practices are generally technical or regulatory measures, while behavioral practices typically involve market-oriented measures. Collectively, these measures, which affect water use and reduce waste and loss from the source, are known as “demand management” measures. Such measures include leak detection; waste reduction (encouraging consumers to cut out wasteful uses); investment in appliances, processes, and technologies that reduce water input without reducing consumer satisfaction and/or output; treatment of industrial effluents and wastewaters to a standard suitable for recycling and reuse; and reallocation of freshwater resources to the area of greatest social good. The policies that encourage demand management include pricing water at an economic rate, charging for pollution or community-based pollution control practices, regulating and restricting specific water uses, exhorting and informing the consumer of the ways and means of use reduction and recycling, and encouraging water trading among and between users.

In Kenya, local NGOs have found that charging everyone the same rate for water leads to many people feeling forced to take their water from polluted sources. Experiments with reduced rates for lower quantities have led to lower rates of abstraction overall and the benefit of greater access to poorer people.