This is a fully operational model of a simple electric circuit using water. Voltage is maintained to ensure constant pressure (simulating a battery or power supply). Voltage across the two variable resistors/switches is visually quantifiable. Voltage across the supply can be varied.
Science is hard, and electricity is especially difficult for students. Not only provide your students with a robust mental model, but generate testable hypotheses to evaluate the model itself - thereby emulating how scientists work. Use the model to predict a suprising outcomes and test these in a real circuit (advanced). Supported with a series of short videos showing how to use this to drive deep understanding from Year 7 to Stage 6 Physics. This provides a great, tangible "hook" and is an invaluable teaching aid for explicitly teaching the fundamental concepts of voltage and resistance and demonstrate how current is the consequence of these two.