Have you spilled over your coffee? Then you'd better pretreat your shirt or blouse before you put it in the washing machine tonight. Water, more specifically raw water, can also be pre-treated before the actual water treatment process. These include, for example, mechanical separation processes, trickling, which can be used to expel the free carbonic acid, or the recently mentioned UV oxidation to reduce the number of bacteria. Exactly which methods are necessary depends on the quality of the raw water available.