A submersible pump assembly for transference of a fluid medium with low viscosity is disclosed. In one embodiment, the submersible pump assembly includes multiple pump units co-axially aligned with a common drive shaft, a common suction chamber, and a common pressure chamber. Each of the pump units includes an active operational mode wherein the fluid medium is transferred from the common suction chamber to the common pressure chamber during as well as an inactive operational mode wherein the fluid medium is circulated through the common suction chamber. Each of the pump units is individually actuatable.