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Expanding water reuse — the
use of treated wastewater for irrigation, industrial uses, and drinking water
augmentation — could significantly increase the nation’s total available water
resources, concludes a new report from the National Academy of Sciences,
titled, “Water Reuse: Potential for Expanding the Nation’s Water Supply through
Reuse of Municipal Wastewater.”
A portfolio of treatment
options is available to mitigate water quality issues in reclaimed water, and
new analysis, the report says, suggests the risk of exposure to certain
microbial and chemical contaminants from drinking reclaimed water does not
appear to be any higher than the risk experienced in at least some current
drinking water treatment systems and may be orders of magnitude lower.
Adjustments to the federal regulatory framework could enhance public health
protection for both planned and unplanned — or de facto — reuse, and increase
public confidence in water reuse.
Key findings in the report
include the following:
• Approximately 12 billion gallons of municipal wastewater
effluent is discharged each day to an ocean or estuary out of the 32 billion
gallons per day discharged nationwide. Reusing these coastal discharges would
directly augment available water resources — equivalent to 6 percent of the
estimated total U.S. water use, or 27 percent of public supply. Inland effluent
discharges may also be available for water reuse, although extensive reuse has
the potential to affect the water supply of downstream users and ecosystems in
water-limited settings.
• De facto reuse of treated wastewater to augment drinking
water supplies — for example, when a drinking water system uses a water supply
that receives upstream wastewater discharges — is common in many of the
nation''s water systems. A systematic analysis of the extent of effluent
contributions to potable water supplies has not been made in the U.S. for over
30 years.
• A portfolio of treatment options, including engineered and
managed natural treatment processes, exists to mitigate microbial and chemical
contaminants in reclaimed water. Numerous process combinations can be tailored
to meet specific product water quality objectives.
• To ensure the quality of reclaimed water, treatment
systems should include multiple barriers for pathogens that cause waterborne
diseases to strengthen the reliability of contaminant removal, and should
employ diverse combinations of technologies to address a broad variety of
contaminants. Reclamation facilities should develop monitoring and operational
plans to respond to variability, equipment malfunctions and operator error to
ensure that reclaimed water meets the appropriate quality standards for its
use.
• In nearly all current potable water reuse systems, water
is discharged after treatment to an aquifer, stream, or a wetland to provide a
buffer between water treatment and consumption. Environmental buffers can
further remove contaminant levels such as pathogens from the water and provide
additional retention time. However, the science necessary to design engineered
natural systems to provide a uniform level of public health protection is not
available at present.
• Modern technology allows the detection of chemical and
biological contaminants at extremely low levels, but the detection of a
contaminant in reclaimed water does not, in and of itself, indicate a
significant risk. Information on the dose of a contaminant required to cause
health effects allows scientists to determine if the level of contaminant is
significant.
The committee compared the
estimated risks of a conventional drinking water source that contains a small
percentage of treated wastewater against the estimated risks of two different
potable reuse scenarios considering 24 chemical and four microbial
contaminants. The analysis suggests that the risk of contaminant exposure in
the two planned potable reuse scenarios does not exceed the risk encountered
from existing water supplies, and may be orders of magnitude lower.
The financial costs of
water reuse vary widely because they depend on site-specific factors, the
report notes, including the location, water-quality objectives, and method of
treatment applied. To determine the most socially, environmentally, and
economically feasible water supply option, the non-monetized costs and benefits
of reuse projects should also be considered.
