English: Scheme of the desalination machine: the desalination box of volume $\Vbox$ contains a gel of volume $\Vgel$ which is separated by a sieve from the outer solution volume $\Vout=\Vbox-\Vgel$.
The box is connected to two big tanks with high and low salinity by two taps which can be opened and closed as desired.
The chain of buckets expresses the fresh water consumption followed by refilling the low-salinity reservoir by salt water.