In the old days in India, when visitors came to your house, you would offer them water to drink and water to wash their feet. That’s because it’s been a long journey in the desert and that’s the first thing they would be dying to have.
When we offer clear and clean water, it helps make our minds clear and alert, so we can understand the Dharma. Pouring the water in the bowls is an act of concentration as we don’t want to spill the water everywhere.
There is a special way of pouring the water and clearing the bowls afterwards.