My anti-freeze is 100% water and now it has a brownish tint to it plus my car always overheats.......we'll leave the CEL and rough driving out of this along with its other minor problems cause I think this would be A bigger problem. Its been like this for months!!
If your running 100 percent water, might be some rust starting to mix in. You really should run 50/50. Check your dipstick and oil fill cap for any buttery churn type substance. If you have it its probably a head gasket.