S8_11-15-04

• Basin: Statewide
• Title: SWSI Phase 1 Report - Section 8 Options for Meeting Future Water Needs
• Date: 11/15/2004
• Author: CWCB
• SWSI - Doc Type: Final Report

aquifers are also recharged by agricultural and urban
return flows and may be high in salts, minerals and
nitrates. Advanced water treatment techniques, such
as reverse osmosis, are commonly used to treat
alluvial aquifer water for M&I use. The disposal of the
waste streams from reverse osmosis treatment can
be very expensive.
^ The recharged water will eventually return to the river
system if not used or recaptured, and so may not be
recoverable when needed.
^ Additional wells may need to be constructed to meet
peak demands.
^ Storage may need to be developed to capture peak
surface water flows that are used for later recharge.
^ A water court approval process, which may be lengthy
and expensive, is required.
8.2.5 Municipal and Industrial Reuse
M&I reuse involves a second or consecutive uses of
consumable water supplies that have first been used to
meet municipal or industrial needs but not fully
consumed. The first aspect important to understand in
reuse projects is the consumptive and non-consumptive
components of water use. Water use is generally divided
into CU (i.e., water that is in effect consumed and
eliminated from the system) and non-CU (i.e., water
returning to the system after use by infiltration into the
ground, or water returning to the system as effluent from
wastewater treatment plants after use in households).
Reuse projects seek to recycle that portion of the water
not consumed.
M&I consumable return flows can be reused through
several methods. Three general types of reuse projects
were included for consideration in the SWSI process:
water rights exchanges, non-potable reuse and indirect
potable reuse.
8.2.5.1 M&I Reuse by Water Rights Exchanges
M&I reuse by water rights exchanges involves the
exchange of legally reusable return flows for water
diverted at a different location. Water is diverted at one
source in exchange for water replaced to downstream
users from a different source. In an M&I reuse exchange,
the amount of non-CU water returned to the system, e.g.,
via effluent flows and/or return flows from landscape
irrigation, depends on the CU associated with the
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Section 8
Options for Meeting Future Water Needs
demand (i.e., the higher the CU, the lower the percent of
total diversions that can be reused).
The non-CU water can be reused multiple times,
theoretically to extinction, with the total available water
reduced with each application, since each time the water
is diverted for reuse, a portion of it is consumed by the
use. A schematic illustrating the exchange of
consumable return flows is shown in Figure 8-4.
The increases in yield that can be achieved through the
successive use and reuse of the return flows to extinction
are shown in Figure 8-5. For example, if there are no
return flows from the use of 1 AF of consumable water,
then there is no additional yield and the total yield is one
acre-foot. If 50 percent of the return flows from an M&I
use of consumable water were exchanged and the return
flows from each successive use used to extinction, the
total yield realized from 1 AF of consumable water is
1.6 AF. This is based on an assumed M&I CU of
35 percent and return flows of 65 percent.
Potential benefits of exchanging reusable flows include:
^ Improves M&I reliability by providing for additional yields.
^ Maximizes water use through successive uses.
^ Maximizes beneficial use of water.
^ May not require additional diversion structures or
other facilities.
^ Lesser environmental impacts than a new water
supply project.
Consumption on Gonsuimption an
Uutdoor Uses Indaor Uses
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Municipaf 8~
~ndustrla~ users
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S:\REPORT\WORD PROCESSING\REPORT\S8 11-9-04.DOC 8-15
Figure 8-4
M&I Water Rights Exchange