|Drinking water disinfection in the USA |
For decades, chlorine has played an important role in water treatment. Chlorine is the most widely applied disinfectant. The advantage of chlorine is that is can easily be produced and that it is relatively cheap. Chlorine effectively kills pathogens. It contributes to the reliability of drinking water produced from surface water. Chlorine tablets are used to disinfect water on locations where no collective drinking water treatment takes place. After the discovery of chlorinated byproducts, the use of alternative disinfectants has increased.
In the United States of America, 50% of the drinking water is produced from groundwater. In some cases surface water from rivers and lakes is used. Chlorine is mainly used for the disinfection of drinking water in the USA. In the past few years alternative disinfectants, for example chloramines, have been used to reduce the amount of disinfection byproducts.
Standards for drinking water disinfection in the USA
In 1914 the first drinking water standard was accepted. The standard concerned the maximum amount of bacteria that should not exceed 100 microorganisms per liter water. Less than 2 coliform bacteria per 100 milliliter water were allowed. In the following years more drinking water standards were established, for example for lead, copper and zinc. Existing standards were intensified. In 1962 there were 28 standards for substances found in drinking water. For health threatening chemical and biological pollutants, obliged maximum pollution values were formulated. For pollutions altering the looks, taste and smell of water, directing values were formulated.
Clean Water Act
The Clean Water Act (CWA, 1972) is an amendment on the Federal Water Pollution Control Act (1948) which contains the basic rules for pollution discharge into water. The CWA was established to repair and preserve the chemical, biological and physical quality of all water (including oceans, lakes, rivers, streams, groundwater and wetlands) in the United States of America. Through the CWA, EPA has gained the authority to establish standards for water pollutions.
Safe Drinking Water Act
The Safe Drinking Water Act (SDWA) was established in 1974. Its purpose is to maintain a safe drinking water quality. The attention for the drinking water quality increased in the United States of America after the discovery of various (industrial) pollutants in drinking water and the discovery of disinfection byproducts.
The EPA establishes drinking water standards to protect public health. To attain these standards, drinking water is treated to remove pollutants and is subsequently tested. Drinking water quality in the USA has improved after the implementation of the SDWA.
Stage I and Stage II Disinfectant / Disinfectant Byproducts Standard
In 1998 the Stage I and Stage II Disinfectant / Disinfectant Byproducts Standard was established. Stage II contains maximum pollution values for disinfection byproducts that can harm human health. The byproducts that are regulated are found in drinking water networks in concentrations which can be harmful (table 1).
Table 1: maximum concentrations of disinfectants and disinfection byproducts according to Stage I and II Disinfectants and Disinfectant Byproducts rules.
| || ||Stage I ||Stage II |
|Disinfectant ||Chlorine ||4 ppm || |
| ||Chloramines ||4 ppm || |
| ||Chlorine dioxide ||0.8 ppm || |
| || || || |
|Byproducts ||Total trihalomethanes ||80 ppb ||40 ppb |
| ||Halogenic acetic acids ||60 ppb ||30 ppb |
| ||Bromate ||10 ppb ||5 ppb |
| ||Chlorite ||1 ppm || |