Chapter 3 Decision Support Model (IUWS-DSM) - Tubdok

Chapter 2 · New Conception 33
Single water system. It is corresponding with the centralised water system, where single
pipe system supplies single water quality. As the highest required water quality in common
situation, drinking water quality is mostly adapted. Single water system has many
advantages comparing to dual water system, like lower construction costs, easier to maintain,
lower risks (i.e. no cross connection issues), etc. Up to now, most water supply systems
worldwide are the single water system.
Dual water system. It is designed for supplying two types of water quality in the same
time. The consideration of dual water system can be traced back as early as 1894 (Haney
and Beatty, 1977). It is especially suitable for the situation that the source water is
quantitatively adequate but qualitatively scarce. A dual water system is usually too expensive
to be afforded because of its doubled pipe systems. However, it also depends on the system
scales and project situations. Leconte et al. (1988) developed both static and dynamic
models for evaluating dual water systems, and made two case studies in West Jordan City,
USA. They proved that the dual water system is economically infeasible for the entire city but
results in positive benefit when it is only for one district in the city area. Certainly, in the
hierarchical system, the dual system can be flexibly applied in the proper places on the
economical scales.
2.2.3.2 planning process
Figure 19 shows the process for planning the desired water system for all types of water
entities. In general, there are two planning steps. First the information and data about quality,
quantity and system options are managed and processed. Second the related water
infrastructure is calculated concerning the cost and energy consumption.
The information of inflow quality is delivered from Subsystem 2 water sources, where the
required outflow quality is based on the outcome from Subsystem 1 water usage. All possible
inflow qualities are identical to the supplied water quality in Subsystem 2, and the possible
outflow qualities are A(1), B/C, and A(1) + B/C (Figure 19). The symbols remains the same
sense, where the symbol of “A(1) + B/C” indicates to use dual water system. Particularly, if
the reclaimed water is directly reused, the dual water system automatically comes forth due
to its non-potable water quality. This situation is explained more in the next section.
Process for Planning Desired Water System
subsystem 3
Desired Water
Inflow quality
raw
B/C
A(1)
raw + B/C
raw + A(1)
B/C + A(1)
step 1
Outflow quality
A(1)
B/C
A(1) + B/C
Treatment
no
yes
step 2
Figure 19: Process for planning desired water system
Distribution
single
dual