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

2.1.4.1 water quality
Chapter 2 · New Conception 13
Due to the attributes and purposes, three sorts of water are classified, i.e. Raw Water,
Desired Water and Used Water. Raw water refers to the water directly comes from the
nature, such as surface water, groundwater and rainwater, etc. As mentioned above, used
water is used to substitute for the conventional term “wastewater”, involving different types of
urban sewage. Desired water has the quality that satisfies the requirements of the end uses.
As an example, potable water is one type of desired water. Three sorts of water have certain
types of quality that can be converted to each other through either treatments or uses. The
relationships between water qualities are depicted in Figure 7.
Relationships between Different Types of Water Quality
RAW
water quality
supply water discharge
water uses
recover
treatment
supply
DESIRED
water quality
natural
water body
treatment
treatment
USED
water quality
Figure 7: Relationship between different types of water quality
Raw water quality. It is for describing the fresh water, which helps to determine whether
the source water is suitable for the urban use purposes, as well as to determine the proper
treatment methods. Groundwater and surface water are the most common water sources, so
their quality standards and regulations are well established in many countries and regions. In
brief, the raw water quality is usually categorised into several levels based on certain critical
parameters. The local standards and regulations have to be obeyed during the water source
selection.
As another type of raw water, rainwater usually has very good quality before rain reaches
the ground. The human beings’ activities cause the environmental pollution and subsequently,
deteriorate the rainwater quality, e.g. acid rain. After rain falls onto ground, the
substances or pollutants on the ground dissolve into the rainwater, which results in the
pollution of rainwater. Different places contain different kinds of substances, so the rainwater
quality is quite depending on its collection places. Normally two streams of rainwater are
distinguished, i.e. Surface Runoff that is collected on the ground, and Roof-water that is
gathered from building roofs. Some measurements of rainwater quality are given in Table 1
as the examples, which are based on the summation from Australian literature. For making
the comparison, the effluent quality after secondary treatment is also listed on the right side
in Table 1. Obviously, the rainfall in areas with limited air pollutants is very clean. Roof-water
has also quite good quality but with the high content of coliforms, which is mostly because of
birds’ excrement on roofs. Surface runoff is even worse because of various pollutants on the
ground in cities.