Can a venturi be used to calculate the flow rate of water out of a 1000ml bottle of water to determine an arbitrary volume left within the bottle? I need to calculate arbitrary volumes of water within opaque bottles of >1000ml without removing or coming into contact with the solution. I need to calculate results electronically so was thinking of using sensors of a venturi of a way of achieving this. Anybody have any advice, or a solution? Thanks. P.s: This is an independent study, not academic.