This book deals with the importance of water, which is one of the natural resources essential to human life and the balance of ecosystems, as well as the economy in the primary and secondary sectors. However, the decline and quality of water has become a global problem that jeopardises human survival, requiring monitoring by the competent bodies and the population in general, since water sources are subject to contamination by pathogenic micro-organisms, responsible for the transmission of waterborne diseases. With this in mind, the aim is to carry out a microbiological analysis (coliforms) of the water distributed from the underground water supply microsystem to homes in the Urumari II neighbourhood in Santarém-PA, where samples were sampled, collected and analysed using the Most Probable Number (MPN) technique using the multiple tube method. In view of the irregularities found, the presence of total coliforms and thermotolerant coliforms does not comply with the maximum legal limits permitted by ordinance 2.914/2011.