If water is on the transmitter and supplements on the receiver, is sitting between the boxes necessary? Wouldn’t drinking the water deliver the energy anyway?

If your goal is to imprint the water, then you do not need to sit between the Scalar boxes. After the water has been imprinted, you can drink it and receive the energetic imprint that has been transferred into the water.

However, if you also want to receive the benefits of the Pure Scalar field itself, then sitting between the boxes is recommended. The two approaches complement each other—one is through the imprinted water, while the other is through direct exposure to the scalar field.

So if time allows, you can certainly do both, but it isn't necessary to sit in the field just for the water to be successfully imprinted.