1. ABNT - Brazilian Association of Technical Standards (1997) NBR 13,969 - Septic tanks - Complementary treatment units and final disposal of liquid effluents - Design, construction and operation (in Portuguese)
2. ABNT - Brazilian Association of Technical Standards (2007) NBR 15,527 – Rainwater - Use of water from roofs in urban areas for non-potable purposes – Requirements (in Portuguese)
3. Almeida OA (2010) Water Quality for Irrigation. Embrapa: Cruz das Almas – Brazil. (in Portuguese)
4. Antas FPS (2011) Avaliação da Composição Iônica e Aplicação de um Índice de Qualidade para Água de Irrigação no Rio Açu, RN. 2011. 67 f. Dissertation of Irrigation and Drainage of Federal and Rural University of Semiarid. Rio Grande do Norte (in Portuguese)
5. Ayers RS, Westcot DW (1999) A qualidade da água na agricultura. Estudos FAO: Irrigação e Drenagem, 29, 2. ed, Campina Grande, UFPB 145p (in Portuguese)