Julie Gillenwater, Division of Drinking and Groundwater, Ohio Environmental Protection Agency
Karen Mancl, Professor Food, Agricultural and Biological Engineering, The Ohio State University
Developing a system to distribute water to customers is a big investment for a community. Because a water distribution system is intended to serve a community for more than 50 years and it is buried and difficult to access, careful planning and consideration is needed.
Water distribution systems have three major components: pipes, valves, and flush hydrants. Each part plays a role in ensuring adequate water service and in maintaining quality water.
Because the pipes and valves are buried, a detailed map is needed to gain quick access to the system for maintenance and repairs. A map is also an important planning tool for upgrades and expansions. It is common for an experienced operator or town employee to have detailed knowledge of the location of all distribution system components. Relying solely on memory, however, can put the distribution system at risk if problems occur when the responsible person is unavailable. A detailed map ensures that the investment in the community infrastructure is documented, and can be studied and shared with interested parties.
Water pipes should be laid out in loops to avoid dead-ends that create stagnant water. Water pipes must be buried at least 48 inches below the ground surface in Ohio to protect them from freezing.
Two types of water pipes are needed in a water system—transmission lines and distribution lines. Transmission lines are the pipes that carry the water from the source to the storage system. Transmission lines are the largest, thickest pipes in the system making them the most expensive. When planning a water system, try to keep the treatment and storage tanks close to the water source to reduce the cost of transmission lines.
Distribution pipes carry water out to the users. To protect water quality, water pipes must be at least 10 feet from sewer pipes and laid in separate trenches. The absolute minimum diameter for a distribution pipe is two inches. A six-inch diameter pipe is the minimum needed for fire flows and for serving fire hydrants.
Since water pipes will be used for at least 50 years, most communities look ahead to expanded service and often use bigger pipe than the minimum. Too large a pipe, however, can lead to water quality problems. If water stands too long in large pipes, the chlorine residual diminishes, metals can dissolve in the water, and biological films can grow.
Values are a critical part of a water system and are often an afterthought. Valves isolate portions of the water system for servicing. By carefully considering the placement of valves, water system repairs and maintenance can be conducted with minimal loss of service.
Valves that are not used for years may not function when the need arises. Valves can stick and even break if neglected. A valve exercise program is a necessary part of water distribution system maintenance.
Flush hydrants are the most visible part of the water distribution system. They must be at the end of all lines to remove accumulated corrosion products from dead-ends. Flush hydrants should also be installed throughout the system to provide for periodic flushing to maintain high water quality. Sometimes people mistake flush hydrants for fire hydrants. Fire hydrants are larger and are often connected to larger pipes.