A heat pump apparatus module for heating and/or cooling supply water, the heat pump apparatus module including: an apparatus housing at least partly provided with an outer wall; a heat pump arrangement including a condenser, an evaporator, and a compressor arranged between said condenser and said evaporator, said compressor configured to transfer a heat transferring medium from said evaporator to said condenser; wherein said heat pump apparatus module is divided into at least two separate compartments being: an air-flow compartment including a first heat pump component being either the condenser or the evaporator, and being configured to allow air to flow through said air-flow compartment, said first heat pump component configured to utilize said air for heating or cooling said heat transferring medium; a first closeable compartment being accessible through a first closeable opening.