I'm sorry, but where did the 2 inches of water come from? If you started filling at 11 am, at what time did you check to find the 2 inches of water? At 1 pm (2 hrs later), you measured 5 inches in the tub. So, you are either putting 3 inches or 5 inches of water in every 2 hrs. You have a span of 6 hours from 11 am to 5 pm, so go figure.