The problem is if they use that water we saw on ANY of their farms , we can not differentiate which were irrigated with good water and which weren’t.
Methane isn’t a toxin, these people are toxicologists who look for dissolved metals, most of which constitute industrial waste. And ‘testing for molecules’ doesn’t make sense since these organic molecules are what makes plants grow unless you mean to assume that people drink this water without boiling, otherwise toxic dissolved metals are the most critical components.