Abstract: Certain aspects of natural gas liquid fractionation plant waste heat conversion to simultaneous power and potable water using organic Rankine cycle and modified multi-effect distillation systems can be implemented as a system that includes two heating fluid circuits thermally coupled to two sets of heat sources of a NGL fractionation plant. The system includes a power generation system that comprises an organic Rankine cycle (ORC), which includes (i) a working fluid that is thermally coupled to the first heating fluid circuit to heat the working fluid, and (ii) a first expander configured to generate electrical power from the heated working fluid. The system includes a MED system thermally coupled to the second heating fluid circuit and configured to produce potable water using at least a portion of heat from the second heating fluid circuit. A control system actuates control valves to selectively thermally couple the heating fluid circuit to a portion of the heat sources of the NGL fractionation plant.