Control of Corrosion and Scaling. A primary goal of water treatment is to
produce stable water--that is, water that is neither corrosive nor scale-forming.
Meeting this goal is not always easy. The focus of this section is on the characteristics
and control of scale and internal corrosion of pipes. Control measures for external
corrosion of pipes, tanks, equipment, and structures is covered in Section 11. For
information on the chemistry of corrosion and scale formation, control methods, and
chemical handling and storage, as well as guidance in selecting a control process, see
pars. 2.1.5 and 2.2.68.
In 1991, the USEPA enacted a regulation called the Lead and Copper
Rule. This rule is designed to reduce exposure to excessive lead and copper in
drinking water. Detailed information on the Lead and Copper Rule, including
monitoring and testing, can be found in pars. 2.2.48, 2.2.49, and 2.2.50. These
sources also provide guidance on developing control strategies.
Iron and Manganese Control. Iron and manganese are natural
reservoirs. These elements are not normally harmful to human health, but relatively
small amounts of iron and manganese can give water an undesirable taste, discolor
plumbing fixtures, and stain laundry. Paragraph 2.1.5 describes control measures for
naturally occurring iron and manganese in raw water supplies. Controlling iron that
results from corrosion of distribution systems is covered in par. 5.4.7.
Lime Softening. Certain dissolved minerals, mainly calcium and
magnesium, give water the property known as "hardness." Hardness is a folk term
inherited from when it was difficult or "hard" to wash with highly mineralized waters.
While hardness minerals are not at all harmful to human health, they can cause scaling
and adversely affect aesthetics. Reducing minerals that cause hardness is called
"softening." The focus of this paragraph is on lime and lime-soda softening. Other
processes used for softening are ion exchange and membrane treatment. Ion
exchange softening is covered in par. 5.4.10; membrane technology is covered in
par. 5.4.13. Besides the general topics, subjects covered include basic chemistry of
the lime-soda process and recarbonation, as well as description of treatment facilities.
Refer to pars. 2.1.2 and 2.1.5 for further discussion of these topics. Maintenance of
lime slakers is discussed in par. 11.8.2.
Ion Exchange Processes. Ion exchange is a common alternative for lime-
soda softening, especially for small water systems or for systems with dispersed water
sources, such as supply wells. Ion exchange can also be used to demineralize water
completely, but the focus of this paragraph is on softening. Paragraph 2.1.5 includes a
description of the process and facilities, process chemistry, health concerns,