Treatment and Popularity of Re-Using Onsite Water
Each treatment situation involving the use of onsite water is unique and must be approved by the authority having jurisdiction. At the same time, the re-use concept is growing in popularity and the nation's major plumbing codes have adapted to it.
Each situation is unique and must be approved by the authority having jurisdiction. The type of treatment needed depends on the intended end use of that water. For example, rainwater and air conditioning condensate can be used in cooling towers with little (if any) treatment as long as the tower has a good biocide treatment system. But rainwater and condensate should be disinfected before being used for above-ground spray irrigation.
By contrast, if on-site wastewater is recycled, it must have full biological treatment followed by filtration and disinfection. Some sources that typically have higher salinity such as cooling tower blowdown and reverse osmosis reject water can only be used where the higher salt content is acceptable. In summary, each source will need to be evaluated. Treatment levels should not exceed the need for the intended use, otherwise money is being wasted.
The use of alternate on-site water resources is growing rapidly. In some cities, such as San Francisco and Tokyo, it is the least expensive way to provide services to congested downtown high-rise buildings. In these cities, owners are strongly encouraged to use on-site sources of water for non-potable uses within the building. In Tokyo, the use of on-site sources of water accounts for as much 60 percent of non-potable uses in downtown commercial facilities.
Other building and campus managers collect and reuse water for economic and environmental reasons. The University of Texas at Austin collects some 130,000 gallons of water per day on average from air conditioning condensate, foundation drain water, rainwater, and other sources for use as makeup water for cooling towers. The campus supplies the remaining cooling tower makeup water from the City of Austins reclaimed water system. Many other examples can be found nationwide.
New Codes and Standards
Both of the nations major plumbing codes the Uniform Plumbing Code and the International Plumbing Code now have language to allow for the use of alternate on-site sources. Both are also revising their green supplements next year to protect the health and safety of the user.
The U.S. Environmental Protection Agency promotes the use of both municipally reclaimed water and alternate sources. And many of the new stormwater standards and regulations across the nation promote rainwater harvesting, storage of precipitation in the soil profile, and similar measures. Many others are setting standards to facilitate the use of alternate sources of water. In many cases, local jurisdictions may not have caught up with these changes, but at the national level the ground is being set.
Although net-zero water is not feasible for all facilities, it is an idea that is gaining traction for reasons ranging from the need to defray the rapid rise in water and wastewater costs to the value of implementing sustainable practices. Facility owners and managers need to add this arrow to their quiver of tools to use when making sound financial and environmental decisions about their operations. n
Bill Hoffman, senior technical advisor for Water Management, Inc., has more than 40 years of water conservation and water resource planning experience. He has been involved in developing water conservation legislation and new rating tools for both the U.S. Green Building Councils LEED program and Green Globes. Hoffman can be reached at firstname.lastname@example.org.