We recently published an article on how water quality affects herbicide performance. It is written in scientific jargon. At some point we might move toward a NC Extension guide but there are no plans for this in the near future. This is also posted on the Water Resources site. Here is the description on that site and the link to the actual paper.
Herbicide performance can be affected by a wide range of factors. One key factor is the quality of water that delivers the herbicide. At the link below you can find detailed information on how some herbicides are affected by spray solution pH, hard water, turbidity, and other constituents often found in water. This article is published by the Weed Science Society of America in the journal Weed Technology.
Water Resources – Spray Water Quality and Herbicide Performance: A Review