Page 171 - WaterSense at Work

October 2012
Commercial Pool and Spa Equipment
contact with air. Table 5-2 provides an overview of evaporation losses for various pool
sizes, as estimated by CUWCC.
These estimates show that water losses from evapo-
ration can be significant. For example, the total volume of water lost annually in spas
is several times larger than the volume of the spa itself. For larger pools, this effect
is reduced; however, the water loss still can be significant and of the same order of
magnitude as the volume of the pool itself.
Table 5-2. EvaporationWater Losses by Pool Type
Pool Type
Pool Volume (gallons)
Water Loss (gallons per year)
Hotel (in-ground)
Public (in-ground)
Olympic (in-ground)
Filter Cleaning
All swimming pools require pool filtration systems in order to keep the water free
of particulate matter. These systems include pumps, filters, drains, and skimmers.
In terms of water efficiency, the distinguishing factors are the type of filter and the
amount of maintenance associated with it. The other components of the filtration
system have little impact on water use.
Pool filters are differentiated by the media used to treat pool water. These media pri-
marily include sand, sorptive media (i.e., pre-coat filters), and cartridge filters. While
these filter types operate on the same principle of circulating water through filter
media to separate suspended particles, their design differences affect how often
they need to be cleaned, which in turn affects how much water they use. Each type
requires a trade-off between water and material use efficiency.
Pool and spa filters must be cleaned on a regular basis to maintain efficiency. As de-
bris builds up on the filter, water flow becomes restricted and reduces filter efficien-
cy, performance, and sanitation. For this reason, filters must be cleaned regularly. The
rule of thumb is that filter cleaning is necessary after the filter pressure has increased
by 5.0 to 10.0 pounds per square inch (psi).
Pool operators must backwash sand and sorptive media
filters to clean them. During this process, water is run back-
wards through the filter to remove the accumulated debris
and particulates from the filter media. The filter backwash
water is typically drained to sanitary sewer lines.
Sand filters are composed of silica sand, zeolite, or crushed
recycled glass, while sorptive media filters have a diato-
maceous earth, cellulose, or perlite base. Sand filters can
be backwashed several times before the media must be
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Page 19.
Southern Nevada Water Authority. How to Drain a Pool or Spa.
Commercial pool