The Stability of Turbidity in Raw Water and Its Relationship to Chlorine Demand

In this study, 160 raw water samples collected throughout the United States were examined for chlorine demand, turbidity, and other chemical parameters to determine whether these parameters were interrelated. After raw water samples were examined, they were filtered through 0.45‐ μ m membrane filters, and the filtrate and residue were then analyzed. Other parameters such as total organic carbon, total Kjeldahl nitrogen, volatiles, suspended solids, particle size, and inorganics were also examined. Eighty‐nine of these samples were also examined over a one‐week period to determine the stability of the turbidity values over one, three, and seven days. Changes in turbidity were on the order of 77 percent of samples in the range of 0.05–1 ntu, 90 percent of samples in the 1‐5 ntu range, and 96 percent of those >;5.0 ntu. In some cases, more than a 200‐percent change in turbidity is reflected. In 63 percent of the samples, changes of 10–50 percent were seen. Because of this strong indication of inherent instability of turbid raw water samples, measurements of samples should be done immediately on site to ensure accuracy of turbidity readings.