Chapter 2 Clean Water?.pdf

Chapter 2 Clean Water?.pdf - CHAPTER 2 CLEAN WATER What...

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CHAPTER 2: CLEAN WATER? What makes water ‘not clean’? As we said at the start of the previous chapter, when we say water we mean H 2 O, usually in its liquid form. But if we look closely at any particular sample of water, we would find that H 2 O is just the most abundant of the chemical substances in the sample. Any bit of water actually contains numerous other substances also, which a ff ect the characteristics of the water, such as appearance, taste, smell, toxicity and other qualities. (Even the feel of the water – if you ever have the chance to put your hand through a stream of water from a dehumidifier, which is essentially distilled and therefore contains no minerals, you’ll notice its slippery, soft feel.) Many of the chemicals which are typically in water are beneficial or even necessary, in order for plants or animals to use the water; many of the chemicals commonly found in water are neutral and have no particular e ff ect; but of course many chemicals have the potential to be harmful, sometimes in significant amounts or sometimes in miniscule trace amounts. A great many natural settings contribute dangerous substances to groundwater and surface water. Much of this chapter will be devoted to
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human causes of water contamination, but if we consider contamination to be any occurrence of dangerous or undesirable substances then a quick look at natural causes is warranted. Two of the most common settings for natural-occurring contamination are coastal or evaporative introduction of salts, and hot-water systems which pick up metals and other elements from the surrounding rocks. The Environmental Protection Agency has as one of its primary purposes the guarantee of a public supply of safe drinking water for the country, as set out in Congress’ Clean Water Act (1941, amended 1972) and Safe Drinking Water Act (1974, amended 1996). The Safe Drinking Water Act applies to all providers of drinking water which supply more than 15 connections or more than 25 individuals. (EPA.gov) Interestingly, this mandate does not cover bottled water, which is considered part of the food supply and is therefore covered by the Food and Drug Administration. Under these acts, the EPA has a specific list of substances (contaminants) which it monitors in our drinking water supply. This list includes seven microorganisms, seven disinfectants and disinfection byproducts (chlorine, etc.), sixteen inorganic chemicals, 53 organic chemicals and four radionuclides. The substances on this list
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come under the National Primary Drinking Water Regulations, because they have the potential to be hazardous to human health. Substances on the National Secondary Drinking Water Regulations have aesthetic (taste, smell, color, etc.) impact rather than health impact (though some of those substances may additionally be hazardous at much higher levels), and will be discussed later.
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