How did the sewage line breaking cause mud in your tap? black/white water lines should never be mixed. For my second sink in my kitchen I have a 5 stage filter

How did the sewage line breaking cause mud in your tap? black/white water lines should never be mixed. For my second sink in my kitchen I have a 5 stage filter system. It goes through a UV light to kill living things, then a 3 charcoal filters, one for large particles, another for removing chlorine and the third for removing small particles. Then it does reverse osmosis before heading to the tap. As far as size, it takes up about 1m x 0.5m x 0.5m