Brimstone Concentration may be used to convert a body of water to sulfurous water. The Titration Protection Act makes use of this technology illegal unless specifically allowed by law.
To make a sulfur pond, first get a law passed. Next, while standing by the pond, select "Special," then "Ecology," then "Initiate Brimstone Concentration." You will then be asked for one left brimstone catalyst and one right brimstone catalyst. The easiest tinctures to make are AfHr for the left and AfBn for the right.
After doing this, you will get the message "The tinctures spread over the water, releasing the smell of rotting eggs. At least you won't have to run very far for sulfurous water now." The water does not turn yellow.