How to make clean water from dirty water?

Depends on what is making the water dirty. If the water was soil and other sediment, filter it. If you have a fear some nasty germs are in the water, boil it, or scrub it with chlorine like is done with tap water. If there is salt in it, desalinate it (using reverse osmosis is best because it removes sediment and nasty germs at the same time). Hard water can be softened by scrubbing with some specific gases too (forget what ones though). If it has been still (and taken up the taste of the container etc.), then the water can be aerated or scrubbed. If the water has high PH, you can filter the water to lower it. If their are elements in the water that are dangerous (like Lead or Copper) you will need to create a reaction with the undesirable elements to filter it out of the water. If the water is holy, the pope can decree it not so, or you could just filter or boil it.

Iodine tablets, I think.

What sort of dirty water!? you really need a filtration device, you can find these everywhere, even Kmart! If yu mean you want to take water from a bush dam and drink it, Just boil it!

Filtration or distillation