Can you desalinate or distill water with a Peltier module?
solar panels are about 20% efficient, while thermal collectors are about 60% efficient. unless you can get a energy efficiency ratio 3 from the peltier you'll get better performance by just using the sun's heat directky to evaporate the water.
Admittedly the termerature difference between the condenser and the boiler will be fairly small so a high efficiencty may be possible, but peltiers have a failry high electrical resistance so the large current needed to move the large amount of heat will require a large peltier device to minimise the resistive losses.