Use Pythagorean theorem in mathematics to solve this problem. Luolian is a right-angled side of a triangle, which is 0.5 feet long. The other right angle side is the neck of the water, which is the depth of the water. The hypotenuse is also the distance from the shower head to the lotus root. In the poem, it is 2 feet, and the answer from Pythagorean theorem is: 3.75.