Your tank should have a 4' by 4' square base (4' means 4 feet). Determine how high the water will be in the tank. Label this calculation "Water Height" and include this calculation on the design sheet. When the teacher falls in the water level will rise due to displacement. Determine how high the water will rise (assuming the teacher is entirely submerged in the water). Label this calculation "Displacement Height" and include it on the design sheet. Since you want to keep water from splashing out, add an additional foot to the tank height (beyond the displacement height). Determine the height of the tank and label this calculation "Tank Height" and include this calculation on the design sheet.