Christopher J. Webb, PE
Chris Webb and Associates, Inc., PS
Bellingham, Washington
www.chriswebbpe.com
Cisterns for Stormwater Detention, Rainwater
Storage, and Re-Use
Seattle, WA – October 17, 2007
! Global warming is underway and the effects
are being felt locally
! Almost everywhere in the Cascades,
snowpack has declined markedly since
1950.
! Nearly every glacier in the Cascades and
Olympics has retreated during the past 50-
150 years in response to warming.
! For a warming of +4.1°F, which could occur
as early as the 2040’s (but probably not
until later in the century), October through
March runoff increases by about 25% and
April through September about 25% and
decreases by 21%
INTRODUCTION
Global Warming and the case for conservation
Lyman Glacier, North Cascades
Tolt Reservoir
Source: Puget Sound Action Team & The Climate Impacts Group,
University of Washington
SYSTEMS THINKING
All Water is a Potential Source…
SYSTEMS THINKING
Water Management vs. Water Supply…
SYSTEMS THINKING
Potential Water Sources – Semantics are Important
Water Resources Defined
! Potable Water (Drinking)
! Stormwater (General rainwater run-off from sites)
! “Waste”water (An out-dated term; all types of water
are considered resources)
! Blackwater (Toilet water)
! Greywater (Sinks, showers, laundry, etc.)
! Combined Water (Blackwater & greywater)
! Rainwater (Roof run-off)
! Reclaimed Water (Treated “waste”water)
RAINWATER HARVESTING
Introduction
Opportunities
! Rainwater is a clean water
source available at the site
! Delivered at no cost
! Initial treatment provided by a
very effective large scale
distillation process
! Can reduce potable water
demand and/or reduce
stormwater run-off and address
CSO problems
! Global warming is going to
decrease water supply (and
as a result increase its
cost in the future)
The hydrologic cycle
Challenges
! Storage costs can challenge the cost-
effectiveness of rainwater systems
! Current water prices are relatively low and
do not justify much in the way of water
conservati