Important considerations for water distribution system design

May 10, 2023

Water main is shut down before connecting new water main to isolate the connection point. Once cut, water inside the isolated section of pipe often back-drains into the trench.

Around 2.2 million miles of underground pipes support the drinking water infrastructure system in the United States. The aging water system, however, requires upgrades in thousands of communities across the nation to prevent water main breaks and a daily loss of billions of gallons of treated water. If you are a municipal leader, it can be challenging to decide whether to implement upgrades or design a replacement distribution system for your community.

Below, we discuss basic factors that can influence conceptual or design decisions for water system upgrades or replacements, aspects to consider while developing system layout plans and why you need to partner with a team of water engineers to ensure successful outcomes.

Planning a water distribution system design: factors to consider

The water main is installed on a bed of aggregate while crews connect fittings and tracer wire. The pipe will be backfilled with layers of compacted aggregate.

Whether your community needs an upgrade, an expansion or a replacement system, planning is critical for designing an effective water distribution system. Beyond primary concerns, like availability, reliability and quality of water in an area, the community size, type and average usage can also guide water distribution system designs. After initial project review comes layout and permitting, followed by design plans and production. Construction only commences after these planning stages are complete.

Design elements can be significantly influenced by certain factors. The table below lists important details to consider, and explains why and how they might shape the initial designs of a water system during the planning stage.

Important considerations for designing a water distribution system
FACTOR	WHY	HOW
Age	Built in the 1970s and 1980s, the average water network pipe is about 45 years old. Some U.S. systems have pipes topping the century mark.	Replacing worn components in older systems must be a priority.
Geography/climate	Textreme temperatures, topography, elevation, soil composition and local geology influence decisions about installation and materials.	Varying elevations need greater pumping capacity than flat terrain. Freezing temperatures influence choice of pipe materials and installation depth.
Water usage	Partial service line replacements may increase lead levels in drinking water if they disturb lead-bearing pipe scale — the build-up of minerals coating pipe interiors.	Critical factors affecting distribution pipe size and storage and pumping facility size include: Average Day Demand. Peak Hour Demand. Fire Flow Demand. More demand = greater capacity.
Environmental requirements	Local, state and federal regulations dictate minimum drinking water quality. System design standards may include permits for installation, excavation and offset distances from other facilities.	Designs must meet state and local standards for water quality and distribution systems — which may differ from federal regulations.
Project budget	Building or expanding water distribution systems is an expensive project that requires significant funding.	The project budget in terms of funding and costs determines the scope of the project. Funding could be shared by the customers or funded through grants or government revolving loan programs. More money = broader scope.
Demand forecasts	Projections for population growth and fire protection requirements should influence designs for water distribution systems.	Design plans must include elements of expansibility to accommodate increasing populations. More money = broader scope.

These initial design considerations, in turn, determine the layout of a water distribution system. Below, we discuss common system layout types, configurations and the roles of various accessories, also known as appurtenances.

Key aspects of water distribution layout design

Protected water main in water distribution layout.

Following Environmental Protection Agency requirements, casing pipe is used to protect the water main when crossing close to utilities (PVC casing, as shown). This protection is for structural stability and to avoid potential contamination. Pipe supports between the crossing pipes were added later.

The layout of a water distribution system involves input from several teams, including the utility engineering department, engineering consultants, distribution operators or field operators, and others. Most design input focuses on the logistics and implementation of a water distribution system.

Layout

The distribution layout of a water system includes disinfection treatment facilities, pipelines (mains and services), and appurtenances like valves and fire hydrants. Engineers typically calculate a water system distribution layout using parameters like:

Flow rate.

Water demands.

Pressure.

Utilities.

Material selection.

Municipal ordinances.

Flow velocity.

Fire flow requirements.

Topography.

Construction budget/funding.

Right-of-way limitations.

Environmental regulations/requirements.

It is worth noting that several of these parameters are usually considered during the initial planning phase, but input from field operators can help refine layout design calculations.

Configuration

Arterial loop systems. This design surrounds the distribution system with a large-diameter water main that provides adequate flow to the interconnecting distribution system from different locations. This layout design creates greater flexibility by supplying water to the distribution system from multiple locations.
Grid systems. This configuration allows water to circulate through the entire system, which is typically fed by an arterial main or a single transmission line. The layout structure distributes water to multiple areas with better quality, pressure and flow rate.
Tree systems. This configuration is fed by one large water main that branches off into smaller distribution mains, which may result in reduced water pressure and flow.

A water distribution system's design is crucial to providing customers with good water quality at an acceptable pressure level. A good distribution system configuration also helps meet the required water demands and limit the number of customers who run out of water during outages. The three most common distribution design configurations are:

Appurtenances

Appurtenances are common accessories of a functional water distribution system that aid the operators and improve the water quality. Examples of such appurtenances include:

Pipes.
Valves.
Elbow and bend fittings.
Service saddles.
Blow-offs.
Fire hydrants.
Air release and vacuum valves.

Once the initial design, layout, configuration and appurtenances are factored into a water distribution system design, the design plan production can begin. With such a long list of influential factors and design aspects to consider before upgrading or replacing a water distribution system, partnering with a trusted and experienced team of water engineers will make things easier for you.

How Fehr Graham helps design water distribution systems

Fehr Graham is committed to helping municipalities provide safe drinking water for their communities. Whether it is upgrading a water distribution system or replacing lead service lines, our team is available to help you navigate every step of your project. From securing funds for a water distribution system project to planning, designing and overseeing construction, we are dedicated to upgrading aging water infrastructure across communities in the U.S.

To learn more about water distribution system designs and how Fehr Graham can help you upgrade the water distribution system in your community, contact us or give us a call at 815.235.7643.

Derek Thompson, PE, is a Professional Engineer with a proven track record in water, sewer, transportation and site design. He is also the Branch Manager of our Freeport, Illinois, office. Derek is client-focused. He builds and maintains strong relationships with community and municipal leaders while tailoring projects to their needs. Reach him at This email address is being protected from spambots. You need JavaScript enabled to view it..