Why does my water shoot up above a tool when a tool touches it?

I have no idea why this is happening. Everything about the script works fine, just everytime a tool touches the water, the water shoots up. Here it is:

local brick = script.Parent
brick.Position=Vector3.new(-35.5, 1.301, -12)

waveSpeed = 0.1
waveHeight = 0.005

while wait(0.1) do 

for I=1,20 do 
brick.Position=brick.Position+Vector3.new(0,-waveHeight,0) --Lower water
wait(waveSpeed)
end

wait(1)

for I=1,20 do 
brick.Position=brick.Position+Vector3.new(0,waveHeight,0) --Raise Water
wait(waveSpeed) 
end 

brick.Position=Vector3.new(-35.5, 1.301, -12)

wait(1)

end