How do I make a brick that slowly kills? (Please help I've been waiting)

I wanted to make a brick so when you are on it, it slowly damages you as long as you are on it. For example, you're head is in a water brick and you are supposed to drown, right? So you slowly lose 5 health until you die as long as your head is underwater. How can I do this? This is my script and it seems to not work.

function onTouched(part)
	local h = part.Parent:findFirstChild("Humanoid")
	if h~=nil then
		for i = 1, 2000 do
			wait(1)
		h.Health = h.Health - 5
		end

		
	end
end

script.Parent.Touched:connect(onTouched)