As far as Mormons and coffee go, love them or hate them, they are great record keepers and preservers. You can view scores of pioneer journals online such as this site. The tea came later. Coffee was the beverage of choice until the later half of the trail history. Mormons were much more lax on enforcing their admonitions against drinking coffee and alcohol until safe drinking water became widely available by the late 1870s.
While pioneer journals about the Mormon Trail are relatively common because of their centralized hierarchy where every company was assigned one journal keeper (and many more kept their own journal), those of the much greater traveled Oregon Trail are relatively rare because each company was organized according to the whims of the members.
Many of the individual journals mention the pollution of these rivers due to buffalo crossings. And, while it is true that there was no EPA in those days to take water samples and provide actual data, given the number and concentration of the bison herds in those days, it is a logical inference.
Just go to the website a read a few of the pioneer journals if you need further convincing.
Long Horn’s? Please tell me your joking. Some people raise long horns as a novelty or a Texas tradition but I don’t know anybody who raises them commercially, other than to sell them to novelty buyers.