Onsite Residential and Commercial Reuse Treatment Systems
the minimum materials, design and construction, and performance requirements for
onsite residential and commercial reuse treatment systems. It also encompasses resi-
dential wastewater treatment systems (i.e., those that treat all the wastewater flow
from a residence, similar to the scope of NSF/ANSI Standards 40 and 245) and those
that treat the gray water portion only. Further, gray water systems can be evaluated
for treating bathing water only, laundry water only, or both. Reuse applications of the
treated effluent include indoor restricted urban water use, such as toilet and urinal
flushing, and outdoor unrestricted urban water use, such as surface irrigation.
Condensate From Air Conditioning Equipment
Water vapor in the air condenses as it comes into contact with an air conditioner’s
cooling coils. This condensate must be removed to prevent water from damaging the
equipment or building structure. Most often, the condensate is captured in a drip
pan, where it is then discharged to the sewer system.
The amount of condensate generated depends upon the cooling load, relative
humidity, and make-up air volumes.
Condensate generation ranges from three to
gallons per day per 1,000 square feet of air conditioned space, depending on the
type of building and air conditioning system.
Condensate is generally high-quality
and free of minerals and total dissolved solids (TDS). It is also generated in highest
volumes during periods of high cooling loads, making it a good source for cooling
tower make-up water. For more information on cooling towers, see
Section 6.3: Cool-
Condensate is generally safe without additional treatment for direct use in cooling
towers with biocide control, or for subsurface irrigation. However, condensate can
grow bacteria removed from the air in the building. If the condensate is used for
anything where humans can inhale it or come into direct contact with it (e.g., spray
irrigation), it should first be filtered and disinfected.
Reverse Osmosis System Reject Water
Water treatment systems, such as reverse osmosis (RO) systems that use filters and
membranes to remove impurities, will have a residual stream that remains after the
purified water has been permeated through the membrane. Most RO systems have
a recovery rate between 50 and 75 percent, meaning that 25 to 50 percent of the in-
coming water remains as residual and is rejected from the system.
This reject water
is less pure than the source water entering the system but may still be useable for
NSF International. NSF/ANSI Standards. July 2011. NSF/ANSI 350, Onsite Residential and Commercial Reuse Treatment Systems.
EBMUD, op cit.
AWE. Condensate Water Introduction.
EPA and DOE, EERE, FEMP. May 2005.
Laboratories for the 21st Century: Best Practices, Water Efficiency Guide for Laboratories
AWE. RO Discharge Water Introduction.
Onsite Alternative Water Sources