Membrane distillation (MD)  is a relatively new process that is being investigated world-wide as a low cost, energy
saving alternative to conventional separation processes such as distillation and reverse osmosis (RO). This process
offers some advantages compared to other more popular separation processes, such as working at room conditions
(pressure and temperature); low-grade, waste and/or alternative energy sources such as solar and geothermal energy may
be used; a very high level of rejection with inorganic solutions; small equipment can be employed, etc. The driving
force in MD processes is the vapor pressure difference across the membrane. A temperature difference is imposed
across the membrane, which results in a vapor pressure difference.
The principal problem in this kind of system is the accurate measurement of the recipient volume change, especially at
very low flows. A cathetometer, with up to 0,05 mm resolution, is the instrument used to take these measurements, but
the necessary human intervention makes this instrument not suitable for automated systems. In order to overcome this
lack, a high resolution system is proposed, that makes automatic measurements of the volume of both recipients, cold
and hot, at a rate of up to 10 times per second.