Brazilian urban centers have been supplied by water from some basins, which are facing several negative interventions that are endangering their properties as water quality resources. Such effects have recently been observed at Ribeira de Iguape basin, located on the south coast of São Paulo State, due to the growth of unconformities in the environmental water quality tests control. Much of this area constitutes an environmental preservation system, with just a reasonable sanitation support. All the water treatment plants (WTPs) in this basin usually discharge large quantities of water treatment sludge to nearby rivers and streams. Few studies have reported the impact of these residues. However, some cities in the basin continue to use river waters for provisioning. On the other hand, high rainfall and wide flow variation of streams due to the tropical weather may minimize potential sludge deposition effects. This work discusses a monitoring study of a WTP on Ribeira de Iguape River, to evaluate the possibility of this continuous discharge, and search for new alternatives of disposal and treatment of water works residuals, according to environmental patterns.