be a cause. Potability is not normally affected by the presence of odors and taste. On the other hand,
palatability is frequently affected, particularly when a substance such as bone or fish oil is present.
Water containing one of these substances in noticeable quantities is unpalatable. Tastes and odors,
which make water unpalatable, must be removed.
(4) Temperature. Warm water tastes flat. Lowering the temperature of water suppresses
odors and tastes and, therefore, increases its palatability. In the summer the temperature of deep lakes
and reservoirs decreases sharply from top to bottom. By shifting the depth of intake, it may be possible
to draw relatively cool water even during hot weather. Cool water is more viscous than warm water and
thus is more difficult to filter. Cool water is more difficult to coagulate and effectively chlorinate than
warm water due to slower reactions. Expect water production rates to drop as the temperature of the
source water drops. This is important for ROWPU operations because the permeate recovery rates are
also reduced as water temperature drops.
b. Chemical Characteristics.
(1) Acidity and Alkalinity. Some impurities cause water to behave as either an acid or as a
base. The degree of acid behavior is called acidity. The degree of basic behavior is called alkalinity.
Since either condition has an important bearing on water treatment, the degree of acidity or of alkalinity
must be determined. The pH value is a measure of the acidic or alkaline nature of the water. The pH of
water is technically defined as the negative logarithm of the hydrogen in concentration. The pH value
ranges from 0 to 14. A value of 7 is neutral. Values decreasing downward from 7 represent increasing
numbers of hydrogen ions. Values increasing upward from 7 represent decreasing numbers of hydrogen
ions. A high pH value indicates a very strong alkaline solution. A low pH represents a very strong acid
solution. The alkalinity of water is defined as the amount of "alkaline" substances present in a given
sample of water when titrating downward to a pH of 4.2 with sulfuric acid. The acidity of water is
defined as the amount of "acid" substances present in a given sample of water when titrating upward to a
pH of 4.2 sodium carbonate. The pH value of natural water may vary from 3.4 to 9.0 depending on the
impurities present in the water. The pH influences the corrosiveness of the water, the amount of
chemical dosages necessary for proper disinfection, and the ability of the analyst to detect contaminants.
(2) Arsenic. Arsenic can be preset in natural water sources is a wide range of
concentrations. It can come from either natural or industrial sources. Ingestion of low concentrations of
arsenic can cause nausea, vomiting, abdominal pain, or nerve damage. In high enough doses, it can kill.
The standard for arsenic was set up to ensure that no adverse health effects would occur to degrade
(3) Cyanide. Cyanide can be present in natural water. It can come from industrial sources,
such as metal processing, coke production, mining, or photograph development. Chlorination of water
containing hydrogen cyanide results in the formation of cyanogen chloride, a toxic chemical agent.
Ingestion of low concentrations of cyanide can cause headaches, nausea, or nerve tremors. In high
doses, cyanide can result in convulsions, paralysis, respiratory arrest, or death.