Hard to know exactly what the contaminants are. I think just sediment that has accumulated over the almost 40 years of them being water tanks.What kind of contaminants appeared in your water system? Do you have any kind of filtration?
I just have a screen that does, indeed catch stuff. I should add a real filter.
I have a screen filter prior to the high pressure pump and then a really good filter post high pressure pump. So all water in my boat is filtered. Practical Sailor did a 3 book series on water systems. They reviewed all sorts of water filters. I got their most highly recommended filter. Great filter!
dj