UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                     GUIDANCE FROM HOTLINE COMPENDIUM
                                                                             WSGH33
                                                                Date Issued: August 1991
                                                           Date Revised: December 1999

SUBJECT:   Applicability of the SWTR and IESWTR to Seawater Systems*

SOURCE:    Clive Davies

How are systems, whose source water is seawater, regulated under the National Primary Drinking
Water Regulations (NPDWRs)?  In order for seawater systems to convert source water to
potable water, a desalinization process must be applied.  Distillation and reverse osmosis are the
common methods for desalinization of seawater.  Considering the special treatment required for
seawater systems to produce potable drinking water, what, if any, regulations apply?   For
example, are seawater systems required to comply with the Surface Water Treatment Rule
(SWTR) and the Interim Enhanced Surface Water Treatment Rule (IESWTR)?

      Response:

      Treatment for "Surface water" is regulated by the SWTR and IESWTR.  The definition
      of surface water for these rules is water open to the atmosphere and subject to surface
      runoff.   EPA believes that seawater sources are not, by virtue of their depths  and volume,
      generally affected by surface runoff. Accordingly, such sources would not come under
      the definition of "surface waters."  Moreover, seawater sources of drinking water are
      generally treated by distillation or through reverse osmosis.  These processes achieve a
      removal or inactivation of viruses and Giarda cysts that far exceeds the levels required
      under the SWTR.  Additionally, the health risk from pathogens is generally much less
      significant in seawater than in fresh surface water sources.  Typically, pathogenic
      organisms are quickly inactivated in sea water due to the high salt concentration.  Also,
      the rate of dilution of pathogens released into sea waters is generally much more
      substantial than in fresh waters.

      Once a state adopts regulations,  interpretation of definitions and the scope of State
      regulations is left to State discretion as long as any changes result in a regulation which is
      at least as stringent as Federal requirements.  EPA recommends to states that public
      water systems using seawater sources not be required to comply with the SWTR.  States
      should, however, ensure that design and operating conditions of systems using seawater
      sources are optimized.

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