If water gets between the top and bottom chambers of your Berkey water filter, it means the bottom chamber is too full. This happens when the top chamber is refilled while the bottom chamber isn’t empty yet. In that case, the water simply continues to filter through, causing the lower chamber to overflow. The excess water then leaks out between the two chambers.
It’s best to fill the upper chamber completely the first time you refill it. Let this water run through. When you notice that the lower tank is almost empty (as indicated by the sight glass valve or the water pressure), refill the upper tank completely. You can do this because the upper tank is slightly smaller than the lower tank, and the filters in the upper tank take up space. The lower tank therefore has excess capacity compared to the upper tank. By doing it this way, you prevent water from leaking between the two tanks.