Irrigation usually involves pumps or some other way of applying pressure to force the water to flow. As for water on smooth even/level floors, have you ever seen a puddle? If the surface is truly level, then the water won't flow, but will settle in a puddle. If you add water to a puddle that is already there, it won't flow, but will spread up to the point that the surface tension can hold it together. If you pour water on one place on the floor, say near a wall, and it flows to the opposite wall, then your floor isn't level. To make water flow, the surface has to slant by at least 2 degrees.
The TOG