Complex sentence: There is a sulfur odor but mineral analysis of the water consistently shows almost no presence of dissolved sulfur, because the sulfur is in the form of the gas hydrogen sulfide, which degasses from the water very quickly.
Split into simpler sentences: There is a sulfur odor, but mineral analysis of the water consistently shows almost no presence of dissolved sulfur. The sulfur is in the form of the gas hydrogen sulfide, which degasses from the water very quickly.