With the ability to provide food and income for the planet, fish farming and fishing, which are already widely practiced activities around the world, continue to grow across the globe. Water quality is essential for this type of activity. Controlling the chemical and physical factors of the water can ensure the success or failure of the farming. There are many ways to analyze water quality, but not all of them are simple or easy to use. The growing use of mobile devices has sought to facilitate this task, increasingly contributing to these and other activities. Aiming to support this evolution, the “Water Quality Monitor” application was modeled and developed, with the objective of providing, in a simple, easy and accessible way, relevant information on water quality scenarios for raising Nile tilapia fish in a cage-net farming environment. The application development methodology was based on the Rational Unified Process, focused on objects within programming and structured by UML diagrams. The final modeling proved capable of supporting the construction of an application to meet the expected requirements for assessing water quality, which during its use, allowed the control of chemical and physical factors of the water, ensuring the success of the creation, or indicating mitigating solutions for the corrections necessary for the process, being later validated in a case study.