Water samples are periodically collected from water before and after treatment, and from water in selected locations in the distribution system. The samples are then sent to government-certified laboratories and tested according to the regulations of the Safe Water Drinking Act. Detailed information can be found on the EPA drinking water regulation website.
Testing is performed for the following categories of contaminants:
A. Bacterial contamination. The objective is to be certain that the water contains no disease-causing bacteria. Water is first tested for coliform bacteria, a test used as an indicator of bacterial presence. If the results of the coliform test are positive, the water is then tested for the presence of E. coli, a type of coliform bacteria that only comes from human feces. The presence of E. coli means that there is contamination from human sewage and therefore pathogens may be present. If the E. coli test is positive, customers must be notified immediately, and steps taken to discover the cause of the problem and correct it.
B. Disinfection by-products. Treatment with chlorine kills bacteria and other microorganisms in the water. But chlorine is a strong oxidant and also combines with any organic substances (that is, invisible small particles originating from living matter and therefore containing carbon) that are in the water. Some of these disinfection by-products, if ingested on a daily basis for many years, can increase the risk of cancer. One way to decrease the amount of these by-products is to decrease the amount of total organic carbon in the water being chlorinated. This is done by pre-chlorination procedures such as filtration. In addition, drinking water is tested at selected locations in the distribution system for the amount of disinfection by-products present. Water samples are taken in locations likely to have the highest concentrations of such substances, If the average level over the previous year is above regulatory limits, customers are notified. and corrective action taken. Disinfection by-products are not tested for in water from places like rest stops or hotels, because people only drink this water for short periods.
C. Lead and copper. Lead and copper are found in water in customers' homes that are so old that they have lead and copper piping. The customer's piping is not the water company's responsibility, but the company periodically tests for lead and copper in the water from the customers' faucets and notifies the customers of the results. The water company also assists by minimizing the amount of lead and copper leaching out of these pipes through controlling the acidity of the water.
D. Inorganic and organic chemicals. The inorganic chemicals tested for, such as arsenic, leach out of surrounding rock formations into well water, and would not be found in lake or river water. The organic chemicals tested for come from manufacturing or agricultural processes, and are not present in a protected water source such as Long Pond.
E. Radioactivity. Here the presence of alpha particles, beta particles, and radon (released from surrounding rock) is assessed. These contaminants would be found in well water, but not in lake or river water.