Is distillation a practical way to purify water in large city?

Answer 1

maybe it is the practical way because it is the simplest way of purifying liquids --------------------- Technically simple, maybe, but practical? Not really. Distillation is extremely energy intensive when done on a large scale because of the high boiling point of water. A medium-population city (~2 million people) uses around 1300 ML of water a day. It takes 4.184 kJ to raise the temperature of 1 kg of water by 1 K. To boil all 1300 ML of water (1300000000 kg) from 25 degrees to 100 degrees just once would need about 407.9 TJ of energy. Factoring in the inefficiencies of the machinary, the energy requirement can go up to 1 PJ, or about 277000000 kW.h or 277 GW.h. Even the largest power plant in the world, the Three Gorges dam, only produces an average of about 221 GW.h per day. Also, 277 GW.h of energy would cost about 19 million dollars at current energy prices. Such astronomical amounts of energy and money required to supply even a medium-sized city precludes the possibility of using distillation as a practical means of purifying water. This is precisely the reason why the world is fighting over fresh water resources, since if distillation can be economically applied to salt water in the ocean to purify it, there will never be any water shortage.