There are areas here that have sulfur and iron in the water. The water is discolored similarly. It smells like rotten eggs coming out of the tap. They say it's safe, but it really stinks, to me.
It's probably sulfate and might be a by-product from fertilizers. I live on the countryside and I've noticed that even if people have their own wells, it often smells rotten eggs if the live near a farming field.
You're probably right about farming chemicals seeping into the water. Our soil, here, is mostly black clay and the sub-soil is limestone, so the metals and their salts are very high. Most everyone has a natural well to tap, if they want. We're on city water, which means lots of filtering, areation and additional chemicals. We cook with it, but we buy bottled water to drink. We go through about four to six five-gallon jugs per week. I've been told I drink too much water, but I need a lot of water to feel hydrated well and healthy.