Reservoirs are water sources in many communities and therefore deserve to be studied. This chapter is therefore focused on a reservoir as a hydrologic unit of study for an evaluation of spatiotemporal characteristics of solute at a typical reservoir in southwestern Nigeria. The reservoir feeder streams and spillway were instrumented with staff gauges and monitored for variations in discharge via velocity—cross-section area method for the 2017–2018 hydrological year. Water samples were collected biweekly, and daytime storm events sampled 54 times were obtained to determine total dissolved solids, pH, and electrical conductivity. Results showed that the catchment is characterized by 70–440 µS/cm of specific conductivity, 6.5–8.3 pH units, and 9.1–1344.5 tonnes of TDS. Total inputs of TDS from the tributaries into the reservoir exceeded the exported by 760.75 tonnes, and 47.2% of the total dissolved solids were sequestrated in the reservoir. The study concluded that reservoirs are vulnerable to the effects of land use/cover changes in the parts of the region, and therefore recommends the need to prioritize ecological restoration of contaminated reservoirs/streams as an important part of water quality control.