Water quality

Another basic question I have. When I was looking at Liquid_Cooler's set up, I noticed that his water was very clean looking, but when I look at others, the water looks polluted and murky. Why is that? Is it an additive that they put in the water or something? Thanks.

Usually the tubing gets murky after you used it for a while.
Brand new tubing looks clear. The water tends to stay clear for a long time.