Purifying / treating large amounts of water?

Question

What are the ways first world countries use to purify / treat contaminated water?

Answer 1

Bacterial Digestion, Oxygenation, Chlorination....if a petroleum product is present the filtering (on site) and heating to perk off lights...if its brine then desalinization ...if its heavy metals (chrome , mercury , selenium ,arsenic ,) diatomacios earth cake filters.....there ya go from the E...