Transcranial magnetic resonance (MR)-guided focused ultrasound (tcMRgFUS) has gained prominence as a technology for treating several brain pathologies. A typical FUS applicator has a large water bolus in direct contact with the patient’s head to provide (i) acoustic coupling to the patient, and (ii) a means to remove heat generated from acoustic absorption in the skull. These water bolus structures can lead to significant image artefacts. Here we use electromagnetic simulations to assess water bolus compartment designs that have different electrical properties. The goal is to downselect a design that produces improved B1+ homogeneity and SNR in a region of interest.