Why does water reduce the coefficient of friction?

Question

The coefficient of friction is usually less between two surfaces when one or both surfaces are wet. What, on a microscopic level, is causing this?

Answer 1

Water is a lubricant, allowing the two surfaces to slide over each other more easily. It isn't the world's best lubricant, but it is better than trying to get the dry plates to ride over each other.
What happens on a microscopic level, is that the surface of any solid substance is actually pitted with craters. They may be microscopic, but they are there. When the two pitted surfaces drag against each other, they create friction. When water is applied to the surface, it fills in the mini-crates and allows the plates to slip against each other with less friction.

Answer 2

What acts like a lubricant. From a microscopic point of view, it allows the 2 surfaces slide more easily over the tiny imperfections that exist.

Answer 3

All liquids are considered uncompressable. That's why hydrolic devices work. The liquid, in this case, water, is pressed between the two surfaces and creates a thin film of fluid. Under the right conditions, it can be as slick as ice. If the conditions are poor, it is more than likely just acting as a very poor liquid lubricant when the two surfaces are still touching.