Jeff Morrison, Assistant Director, Operator Training Committee of Ohio
Karen Mancl, Professor Food, Agricultural and Biological Engineering, The Ohio State University
Water system customers expect an uninterrupted supply of safe water. Water systems must consider the fact that the distribution system, once buried, will be used for over 50 years and will require continuous thought and attention. Water system operators often find themselves choosing between two approaches to maintaining system integrity: 1) reacting only to emergencies, or 2) acting to prevent problems from occurring.
The most desirable approach is to develop an active program of strategies to prevent problems and service interruptions.
In maintaining water system integrity, operators address three issues: 1) water line breaks, 2) flushing water lines, and 3) preventing cross-connections.
Improper installation of water lines is the root cause of most water line breaks. Water lines should be bedded to minimize stress as the ground shifts, freezes, and thaws. Water hammer can also break water pipes. Water hammer occurs when a valve or hydrant is closed too quickly. Accidents also break water lines. Traffic accidents sometimes break off hydrants. Excavations can also hit and break water lines.
Prevention of water line breaks starts with proper pipe installation.
Installers must always follow the manufacturer's recommendations in
bedding pipe, backfill with granular fill, and bury pipes below frost
depth.
Regular valve maintenance guards against rapid shut-offs that cause water hammer. Valve exercise programs are one tool in checking valves on a regular basis.
Detailed information on water line locations aid in the reduction of excavation accidents. Detailed maps are one step. Another strategy is burying labeled, metal tape above the pipe in the trench. It is hoped that the tape will be dug up, identifying the water line below before the pipe is hit as shown in Figure 1. In areas with a high risk for excavation hazard, surface paint marking and signs are tools to warn excavators and prevent water line breaks.
Timely repair of water line breaks reduces water loss and minimizes traffic hazards, especially in winter when ice can form. Remember, operators require special support when repairing water lines. Operators must never repair a line alone! Someone must be standing by in case of an emergency. Traffic control is essential if a portion of the road is blocked to repair a leak.
Water pressure is reduced during a water line repair, creating the opportunity for contamination. The following steps protect the customers during a repair:
Water use varies throughout a water distribution system so sediment can accumulate in spots resulting in taste, odor, or iron problems that inconvenience customers. A loss of chlorine residuals at stagnant spots can result in a public health risk. Flushing the water lines is one tool operators can use to maintain water quality and water capacity.
Water systems develop flushing programs for the following five reasons:
It is important to optimize a flushing program in a water system. Excessive flushing wastes water. Also, operators must take steps to protect pavement and property to reduce damage during system flushing.
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| Flush Hydrant | Fire Hydrant |
Polluted water entering a drinking water supply through a cross-connection threatens the health of customers. Seemingly innocent situations can result in illness and even death. A hose connected to the water system submerged in a puddle, tank, or bucket containing pollutants is an example of a cross-connection. An active cross-connection and backflow prevention program is required to protect the customers.
A water system at a central Ohio mobile-home park became contaminated when a water softener waste line was directly connected to a drain and the sewer backed up. The cross-connection was easily eliminated by installing a proper air gap between the potable water system and the sewer drain.
Water systems are required to have an ordinance to ensure backflow prevention and cross-connection control. The ordinance covers the installation and maintenance of backflow preventers at potential risk locations in the water system, such as:
The ordinance also includes an inspection program to ensure that cross-connections do not occur and that backflow prevention devices are not compromised.