This turbidimeter, donated by Seattle Public Utilities (SPU), is a variable depth instrument for visually determining the cloudiness of a liquid caused by the presence of finely divided suspended matter. The origins of Seattle's public utility infrastructure date back to the late 19th and early 20th centuries when efforts were made to secure clean drkinking water and establish public control over essential services. In 1895, Seattle residents voted to approve financial support to construct the Cedar River water system, and water flowed into Seattle from this watershed starting in 1901. The Water Department oversaw the water system from 1910 until 1997, when SPU was established by consolidating the city's Water Department, Engineering Department, and portions of the Solid Waste and City Light divisions. Today, Seattle Public Utilitiesit provides essential water, sewer, and garbage services to over 1.3 million King County residents .