Why do you put water in the grooves?

This is known as the Ritchie water seal and is patented. The water in the grooves creates an airtight seal to disallow cold air entering the valve chamber. Some people will fill this groove with vegetable oil for easier removal in the freezing months. Without this, we would have to use a gasket. It has been proven that when accessing a unit in winter that has a gasket, the gasket will come apart and have to be replaced.