So then going back to prices, how is the cost of sand filtering down to consumers?
那么回到价格上来,沙子的成本是如何落到消费者身上的呢?
英语百科
Sand filter
Sand filters are used for water purification. There are three main types;
All three methods are used extensively in the water industry throughout the world. The first two require the use of flocculant chemicals to work effectively while slow sand filters can produce very high quality water free from pathogens, taste and odour without the need for chemical aids.