The wastewater treatment by lagooning is a very effective and low cost solution because of both initial implementation and low maintenance. In contrast, this application requires significant areas where the holes for the lagoons are digged, so the cost of the land should be not very high and economical to be excavated. Geomembranes for waterproofing these lagoons must meet special requirements in terms of durability, gas tightness, chemical resistance, even also the requirements of local regulations. The wastewater treatment consists of physical, chemical and biological processes that eliminate contaminants in the water. The goal of the treatment is to produce clean or reusable water separated from its solid waste, which can be given different uses: industry and agriculture.