Water-quality data were collected by the Providence Water Supply Board (PWSB) from tributaries in the Scituate Reservoir drainage area, October 2014 through September 2015 (water year 2015). These data were used to calculate instantaneous loads and yields of constituents in a report by the U.S. Geological Survey. Water-quality samples were collected by the PWSB either monthly or quarterly at fixed stations on 36 tributaries in the Scituate Reservoir drainage area. Water-quality samples were collected following a strict sampling schedule so that water-quality samples would be representative of various weather conditions. Samples were analyzed at the PWSB water-quality laboratory at the P.J. Holton Water Purification Plant in Scituate, Rhode Island. Water-quality properties and constituent concentrations were measured by using unfiltered water samples. These water-quality properties included pH, alkalinity, color, turbidity, and concentrations of chloride, nitrite, nitrate, orthophosphate, and bacteria (Escherichia coli [E. coli] and total coliform).