Water Systems for Small Communities

A Puzzle Guide for Local Officials
Bulletin 910

Sources of Drinking Water for Small Communities

Ron Veley, U.S. Geological Survey

To provide an adequate and sustainable water supply for customers, a water system must develop a water source. The principal water source alternatives are direct use of surface water and ground water, or purchase of water from another water supplier. Water conservation is another option for a community to extend a water source to serve the needs of customers.

Surface Water

The two most common surface water supply alternatives for small communities are offstream reservoirs and onstream reservoirs. An offstream reservoir is an earth structure designed to store water. A pipeline and a pumping station, if gravity flow is not possible, are required to transport water from a natural source to the offstream reservoir. Onstream reservoirs, as the name implies, are designed to impound water within the source's main channel. The main components of an onstream reservoir are the dam (earth, metal, or concrete) and the spillway. Both types of reservoirs can be designed for multiple uses, such as public water supply, industrial water use, and recreation. Onstream reservoirs also can provide flood control.

One difference between the two types of reservoirs is their ability to make full use of the potential water capture rate. The capture rate is a measure of a reservoir's ability to intercept runoff from precipitation and snowmelt. The offstream reservoir's design inhibits runoff as a water-replenishment source.

The principal environmental concern with onstream reservoirs is their disruption of a stream's ecosystem. The onstream reservoir transforms part of a free-flowing stream into a ponded, controlled water source. The transformation changes the nature of the ecosystem, which can lead to losses or changes in the plant and animal species associated with the stream's natural ecosystem.

Ground Water

A ground water supply for a small community typically consists of either two large wells or a system of smaller wells that collectively supply sufficient water to meet community needs. Ground water yields are variable throughout Ohio. Yields in northwestern Ohio are commonly 100 to more than 500 gallons per minute per well, whereas yields in the southeast are more likely to be less than 5 gallons per minute.

Most of Ohio's ground water supply meets the Ohio Environmental Protection Agency drinking water standards without treatment except for disinfection. Some ground water will require treatment to reduce high levels of iron, and softening to reduce water hardness is common. Potential contaminants to water supply sources resulting from human activities include leachate from on-site septic systems, hydrocarbon leaks and spills, brine from oil and gas drilling, toxic metals from mining and industrial activities, and pesticides.

Purchased Water

Some communities choose to purchase water from outside sources rather than develop a new surface or ground water source. The community that exercises this option may give up control over certain aspects of the water supply system and thus may not be an active participant in decisions affecting its water supply. The most notable loss of control lies in establishing water rates.

Water Conservation

One solution to problems of increasing water demand is to try to reduce the demand through water conservation programs rather than seek to meet the demand by developing or expanding water supplies. Supply-side management programs, which reduce water losses in the delivery system, include water audits and leak detection. Demand-side management, which reduces water use by modifying customer behavior, can be accomplished through ordinances, incremental water rates, and education. Successful water conservation programs may reduce revenues initially, therefore a community may need to adjust its water-rate structure so that revenues equal the cost of providing water to its customers.

After: Veley, R. J. 1992. Advantages and Limitations of Water-Supply Alternatives. Water Fact Sheet USGS Open-file 92-119.

Summary of Advantages and Limitations of Water-supply Alternatives

Advantages	Limitations
Surface Water—Offstream Reservoirs
Site flexibility compared with onstream reservoirs Potential for incremental development Selective withdrawal of source water Mitigation of environmental disruption Multipurpose use	Operation and maintenance expenses commonly higher than for onstream reservoirs Lower capture rate compared with onstream reservoirs May require a lowhead dam
Surface Water—Onstream Reservoirs
No pump or pipeline from source to reservoir required Higher capture rate compared with offstream reservoir Multipurpose use	Potential contamination from point and nonpoint sources Dam/spillway expense Environmental disruption
Ground Water
Generally less expensive to develop than surface water Operation and maintenance less expensive than for surface water Environmental disruption associated with surface water development is avoided	Quantity and quality may be inadequate Recharge area requires protection
Purchased Water
Reduced capital expenses No source development expenses Water-treatment facility unnecessary	Loss of autonomy Limited control of water rates
Water Conservation
Increased water source longevity Infrastructure projects delayed Reduced treatment expenses	May reduce revenues initially