The properties and behavior of aqueous solutions–that is, water containing dissolved minerals and other solutes–are vital to understanding natural systems and to developing new technologies for water purification, wastewater treatment, and sustainable industrial processes (Stumm & Morgan, 1999). pyEQL provides object representations for aqueous solutions, creating a stable, intuitive, and easy to learn interface for calculating properties of solutions and dissolved solutes. Its purpose is to save researchers time by making a variety of different models accessible through a single interface and by aggregating hundreds of properties and model parameters into a built-in database.