LEAGUE OF WOMEN VOTERS OF THE NATIONAL
WATER SUPPLY TASK FORCE
DRINKING WATER SUPPLY IN THE WASHINGTON, D.C. METROPOLITAN AREA:
PROSPECTS AND OPTIONS FOR THE 21 ST CENTURY
To the reader: The full text of this report, as well as the text of this executive
summary, may be accessed on the world wide web at http://www.lwv-fairfax.org/water.htm. A limited
number of copies of both the report and the summary are also available from Bob Perry,
Falls Church League, tel. 703-534-5421.
The Washington, D.C. region has expanded dramatically in population and geographic area
in the past few decades. This report addresses the availability of water to meet the long
run needs of the region as it continues to grow. The supply of water varies both
seasonally and from year to year, while demand has grown steadily with the growth of the
region's population. Projections by the Interstate Commission on the Potomac River Basin
(ICPRB) indicate that demand could exceed supply early in the 21st century in the event of
severe drought. This report explains how this could occur and discusses several strategies
which may enable the region to avoid water shortages in case of drought.
In 1997, the region's water system supplied an average of 468 million gallons per day
(mgd). Over 96% of this was provided by three major suppliers; Fairfax County Water
Authority serving most of northern Virginia, the Washington Aqueduct serving the District
of Columbia, Arlington, and Falls Church, and the Washington Suburban Sanitary Commission
serving most of the Maryland suburbs. In addition, smaller water companies serve a few
other jurisdictions across the region.
About 75% of the region's water comes from the Potomac River, and the remainder from
the Patuxent and Occoquan Rivers. A severe drought in 1966, when flows on the Potomac
briefly dropped to below today's production levels, led the region to begin collaborating
on drought management. In 1978, the Low Flow Allocation Agreement was signed, specifying
how water will be allocated among the three major suppliers in case of drought. In the 1
980s, two dams were completed whose reservoirs store water for release into the Potomac in
case of drought. The agreement and the dams were expected to ensure that the region could
handle a severe drought without excessively inconveniencing its population.
Demand and Supply Projections
The region's three major water companies are mandated to assess the supply and demand
for water every 5 years. The 1995 study, prepared by the ICPRB, provides the information
on demand and supply on which much of this report is based.
The ICPRB uses a relatively simple model to project water demand. It considers three
types of water users; single family homes, multifamily buildings, and employees. The study
estimates "water use factors," coefficients indicating the average quantity of
water consumed by each type of user in each jurisdiction. Demand for water is calculated
as the number of users in each category multiplied by the water use factor for that
category and jurisdiction. The projections of the number of users are based on population
projections provided by the local jurisdictions to the Metropolitan Washington Council of
Governments (COG). The ICPRB model assumes that the water use factors will remain constant
throughout the period of concern; that is, consumption per user will not change in the
In addition to the water known to be consumed by households or employees, some water is
not accounted for. This unaccounted for water is attributable to leaks, faulty water
meters, pipe maintenance, and fire fighting. The ICPRB estimates unaccounted water from
historic records. Factoring in unaccounted- for water, the total water demand for each
year in the future is estimated as single family use + multifamily use + employee use +
unaccounted retail water + unaccounted wholesale water.
Water supply projections are based on historical records of both the free-flowing
Potomac River and the inflow and outflow for the reservoirs which currently serve the
system. They also take into account an "environmental flow-by" at Little Falls
Dam of 100 (mad) to protect aquatic life. To determine when supply might exceed demand,
the ICRPB simulated a recurrence of the so-called "drought of record" which
occurred in 1930-31, whose probability in any given year is I to 2 per cent. It is
important to bear in mind that although this probability is fairly low, such a drought
could occur at any time.
Comparison of supply and demand
ICPRB projections indicate that under a reocurrence of the drought of record, demand
would exceed supply in 2035. That is, by 2035 population would be high enough to exhaust
the water supply in the reservoirs; before that year, existing water storage systems could
meet water demand even if the worst drought on record were to reoccur. This projection
assumes that water in the Savage River Reservoir, which is designated for diluting
polluted water rather than for consumption, would be made available in case of drought.
Without that source, the reservoirs could be depleted by 2025.
In practice, the adequacy of water supply would be constrained well before existing
storage systems are depleted. Experience with water shortages is limited; however in the
past one water supplier made plans to impose water use restrictions if storage dropped to
40% of reservoir capacity. The ICPRB projections indicate that under the drought of
record, storage levels could be reduced to 40% as soon as 2015 with the Savage River
Reservoir and 2005 without it. Thus, although an actual deficit in the supply does not
occur in the projections until 2025 or 2035, heightened concern and the imposition of
water use restrictions could occur much sooner. These projections require us to address
the problem now.
Strategies to Prevent Water Shortages
The present study identifies several strategies for responding to the prospect of
future water shortages. These are conservation, identification of new water sources,
reducing waste in the water distribution system, managing growth in the metropolitan area,
and reclaiming treated waste water.
Water conservation involves a combination of measures to reduce water consumption or
slow its growth relative to projected needs. Water prices can be structured to create a
financial incentive for households, manufacturers, and commercial enterprises to reduce
consumption. In commercial and industrial establishments, process changes can offer
cost-effective reductions in water demand.
Regulatory policy can require technologies to reduce water use; for example, building
codes often require low-flow toilets and shower heads in new construction. All of these
measures are accompanied by education efforts to encourage households and businesses to
reduce water use. Demand reduction may also include use restrictions when extreme
conditions occur. Rather than build a supply system adequate to allow lawn-watering during
droughts, for example, a community can consciously choose to sacrifice lawns when a
drought occurs and invest resources elsewhere.
Potential new sources of water include surface or ground water from within the Potomac
basin and transfer of water from outside the basin. One way to increase water supply
during droughts would be to construct one or more additional reservoirs on currently
free-flowing reaches of the Potomac and its tributaries. Although this option has been
routine in the past, today it would likely face intense opposition and practical
difficulties in the Washington area. There has been widespread development both in the
valleys that would be flooded and along potential shorelines in much of the basin. In more
remote areas, there would be intense opposition to impounding free-flowing streams in
scenic areas. Ground water might be obtained from wells in the coastal plain of southern
Maryland. Previous studies have indicated that these might offer a maximum yield of 100
mad, but this would be available under drought conditions only and not as a sustainable
supply. The transfer of water from outside the Potomac basin, a strategy commonly used in
the western United States, would face enormous difficulties and seems unlikely.
Reducing unaccounted-for water
The water utilities consider unaccounted-for water to be the difference between their
production or purchase and the quantity paid for by final consumers. Some of these losses
are attributable to unmetered uses, such as fire fighting, flushing pipes during routine
maintenance, and use in public buildings and parks. Others are due to to illegal hookups
or inaccurate meters. Still others are due to actual physical losses from leaky pipes and
similar problems. Total unaccounted-for water for the three main suppliers in the
Washington area ranges from 10 to 28%. In contrast, the American Water Works Association
considers a 10% loss to be acceptable in a well-run system. The incentive to reduce these
losses depends in part on whether the cost of doing so is less than the cost of producing
additional water. Both the actual losses and the means of detecting and reporting them
differ among the utilities. Therefore, detailed studies of unaccounted-for water leading
to a concerted reduction effort may be justified.
Growth management could limit the increase in regional population and hence the demand
for water. Environmentalists will recognize in this approach the principle of limiting
growth to the natural carrying capacity of the area. Sentiment for limiting growth
fluctuates over time; right now the tools for doing so are more readily available in
Maryland than in Virginia. Nationwide, there is a movement to concentrate new development
in higher density mixed-use centers where infrastructure, including water and sewer lines,
already exists. This results in substantial savings in water use through smaller lawns to
be watered, smaller houses, fewer miles of pipes that may be susceptible to leaks, and
less water used during flushing. While growth controls may be desirable, they are not a
likely strategy for reducing water demand, since they go far beyond the relatively narrow
infrastructure concerns of water supply.
Reuse of waste water
The recycling and reuse of treated waste water is common throughout the country where
surface water is the raw water source. This option is already in use in the Washington,
D.C. area at the Upper Occoquan Sewage Authority (UOSA) treatment plant in Centreville,
Virginia. The Fairfax County Water Authority withdraws raw water from the Occoquan
downstream from the UOSA plant, treats it by conventional methods, and converts it into
potable water delivered to its customers. The reuse of effluent from the Blue Plains
treatment plant on the Potomac estuary downstream from Washington may offer a similar
opportunity. As much as 200 to 300 mad might be pumped upstream and discharged into the
Potomac above the intake used to supply Washington. This would ensure a supply of water to
the Washington Aqueduct and permit higher withdrawals from the river by other users. The
major concern is with this strategy is clearly its health implications. Technical experts
feel that the resulting water can be potable; however, the treatment required may make it
Drinking water shortages may confront the Washington metropolitan area early in the
21st century. This is not a problem which can be put off while the region's jurisdictions
cope with more immediate problems. While this report does not identify clear choices among
the options for preventing water shortages, we can make a number of useful observations:
- Water conservation offers both short- and long-term ways for reducing water use. These
should be considered irrespective of our approach to water supply.
- Exploiting new water sources through construction of new reservoirs or building
large-scale ground-water extraction facilities may face serious difficulties due to
increased population in the areas affected and large-scale land-use changes in recent
- Reducing waste in the distribution systems is a financially viable way to save water
where losses are great and the cost of producing additional water exceeds that of finding
and fixing leaks.
- Growth management could lead to reduced demand for water in the region; however, the
scope of growth management efforts goes far beyond the issues considered in this report.
- Reclamation of waste water from the Blue Plains plant is a technical option which
warrants additional evaluation with current data.
More thorough technical and financial analyses of all the options are needed in order
to make informed decisions about how to address projected water shortages. Concurrently,
there must be broad public discussion of the region's water supply issues involving all
interested stakeholders. As we approach the 21st century, public policy questions like
this one are no longer the purview of water systems engineers alone; they must be
addressed by everyone who has a stake in the outcome.
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