Variation of rainwater quality with precipitation: application to Santa Maria city - RS

ABSTRACT This study aimed to evaluate the quality of rainwater in the city of Santa Maria - RS, to assess the variation of some parameters during precipitation, and to identify the most appropriate uses for rainwater depending on the current standards for the use of rainwater and reuse water. Rainwater samples were collected directly from the atmosphere and a roof in order to analyze the changes in quality after passing the catchment surface. Each sampler was divided into five compartments to collect and store separately the first five millimeters of rain. The quality characteristics of rainwater were assessed using the following parameters: pH, conductivity, turbidity, BOD5, total solids, suspended solids, dissolved solids, and Escherichia coli. In some events iron, manganese, phosphate, ammonia and nitrate were also analyzed. It was observed that the quality of rainwater changed after its passage through the catchment. In raw state, rainwater can be used for non-potable purposes, it being recommended to discard at least the initial 2 mm. If treated, rainwater acquires a quality compatible with other uses, such as flushing toilets and washing vehicles. The behavior of some parameters was sensitive to changes in the precipitation characteristics, and there was a variation in the values related to the increase or decrease in the intensity of rainfall.