Certain implementations of natural gas liquid fractionation plant waste heat conversion to simultaneous cooling capacity and potable water using Kalina Cycle and modified multi-effect distillation system can be implemented as a system. The system includes first waste heat recovery heat exchanger configured to heat a first buffer fluid stream by exchange with a first heat source in a natural gas liquid fractionation plant. The system includes a water desalination system comprising a first train of one or more desalination heat exchangers configured to heat saline by exchange with the heated first buffer fluid stream to generate fresh water and brine.