25 for 25: Safer Drinking Water from Rivers, Lakes, and Reservoirs
By Thomas S. Burack, DES Commissioner
In recognition of the New Hampshire Department of Environmental Services’ 25th Anniversary, over the course of the year, I will highlight 25 agency activities, programs, projects and accomplishments of the past 25 years. This article, the seventh in the series, briefly describes advancements in providing safer drinking water from our surface waters.
No matter how far off the beaten path they might wander, few people today would dip a cup in a mountain stream and think the unfiltered water safe to drink simply because it looked clean. The mantra of ensuring safe drinking water today is the “multiple barrier approach. ” Use the cleanest source that will meet your needs. Maintain the purity of the watershed or wellhead area by keeping out – or at least managing – potential sources of contamination. If the source is surface water – a lake, pond, stream, or river – disinfect AND filter the water to kill or remove any organisms that might cause disease. Test it frequently to make sure your treatment is working. And make sure the water remains sterile until it reaches the tap.
Until the Federal Safe Drinking Water Act was amended in 1986 to require filtration of water from surface sources used by public water systems, it was common for water suppliers to rely on disinfection alone – usually with chlorine – to ensure that drinking water was free of disease-causing organisms (pathogens). The New Hampshire Department of Environmental Services was formed in 1987, but one of its predecessor agencies, the Water Supply and Pollution Control Commission, had strongly encouraged filtration before the 1986 amendments, and water systems were given until 1993 to filter their surface water (groundwater did not need to be filtered and still does not) or obtain a waiver from the filtration requirement by demonstrating consistently high quality source water AND implementing stringent watershed protection measures.
The federal 1989 Surface Water Treatment Rule and the changes it set in motion represent some of the most significant public health improvements in drinking water in the past 25 years. Before the rule came into effect, many water systems in New Hampshire were already filtering their water, but 36 water systems used unfiltered surface water. For some of the latter systems, it was rare but not unheard of in those days to find debris floating in a glass of water filled at the kitchen faucet.
The Surface Water Treatment Rule also established stringent requirements for the degree to which water systems had to kill or remove the protozoans Giardia and Cryptosporidium, which can cause severe gastrointestinal disorders. Both of these organisms are highly resistant to chlorination, so they have to be filtered out if they are present in the raw surface water.
Today a number of surface water systems are coming to terms with enhanced treatment requirements under the second phase of the Surface Water Treatment Rule, which requires additional public health protection measures, including redundant disinfection and limits on the amounts of disinfection byproducts in the finished water. Disinfection byproducts (DBPs) are formed when a disinfecting agent – usually chlorine or a chlorine compound – combines with natural organic compounds in the source water. Common DBPs include trihalomethanes such as chloroform.
The challenge in disinfecting drinking water is to use enough of the disinfecting agent to both kill pathogens and maintain a residual level of disinfectant so that pathogens don’t re-grow in the distribution pipes, while not using too much disinfectant. Too much disinfectant contributes to the formation of DBPs, could present a health risk in itself (the limits for disinfectants in drinking water were tightened up in 1998), and can create unpleasant tastes and odors. DES and water suppliers have responded to this challenge with more sophisticated design and operation of treatment processes – for example, by using a variety of disinfectants at various points in the process, providing higher-level operator training, and stepping up the monitoring and evaluation of pathogens, disinfectants and DBPs in source water and in distribution systems.
Perhaps the simplest way of measuring the success of DES’s drinking water programs over the past 25 years is the fact that, as compared to the water from a mountain stream referred to at the beginning, today nearly 100 percent of us expect clean, safe drinking water when we turn on the faucet. We should all be grateful for the variety of advancements in policy, technology and funding opportunities that have helped us to get to where we are today. It is certain, that we will need similar advancements to maintain the progress we’ve made, and to address any new threats to our drinking water supplies.
Note: For a summary of surface water treatment processes used by public water systems in New Hampshire, see the NHDES fact sheet, “Large Surface Water Treatment Plants in New Hampshire” at http://des.nh.gov/organization/commissioner/pip/factsheets/dwgb/documents/dwgb-13-2.pdf.
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