Creation of rain sewer is connected with dehydration of roads and coexisting objects. The paper presents a discussion upon the issue of groundwater contamination by petroleum compounds and other pollutants from transport based on studies of groundwater within the parking lots. The study included 9 parking areas, including 7 in Bialystok, 1 in a residential area outside of Bialystok in Ignatki, and one in Kleosin. The tested waters were subject to determination of COD, total suspension, and petroleum substances expressed as a mineral oil index. The studies have shown that the concentrations of determined parameters were in most cases proportional to the larger runoffs and concentration of petroleum compounds increased with the increase of suspension. It has been shown that from part of the parking lots, the meteoric water was discharged directly into watercourses and exceeds the permissible limits regulated by the Decree.