What did alkaline water mean in the 19th century

I’m watching the film Meeks cutoff, and there is a scene where they get to a source of water but can’t drink it because its alkaline. What does that mean (I assume that means its got a pH above 7)? And how would they test whether the water was acidic or basic? And why would it even matter? People drink acidic beverages all the time, why would alkaline water cause issues?

Not sure if this answers your question, but water in underground caverns etc (where you get stalactites and stalagmites) is loaded with magnesium which gives you diarrhea.

Alkaline is the opposite of acidic. A moderate amount of acidity tastes good and (depending on the acid) might be good for you, but bases almost always taste bad, and are often poisonous.

If the water is alkaline, you can probably see the white powder around the edge that has precipitated out of the water. This is an extreme example.

It’s not the fact that the water is alkaline or the pH that’s the problem (although very high pH water can be caustic), but the specific minerals involved. Too much sodium, potassium, or magnesium will make the water undrinkable.

In Hollywood folklore, drinking from an alkaline waterhole would cause madness and death. In the real world, it’s pretty rare. There are a number of places named Alkali Springs, or Alkali Flats, Or Alkali Lake, but as far as I know, they are all habitable.

Alkaline water is common in the Intermountain West due to evaporation. Some water gathers in a pool, it dries out, and the salts and cruft concentrate in what’s left. After several rains or floods things can get pretty bad. What actually gets built up in there depends on the water source, the amount coming in, etc. So the Great Salt Lake is mainly known for being salty, not alkaline.

There’s several alkaline areas near the Snake River along the Oregon-Idaho border. The Snake used to flood over shallow areas and dry up. The salt got partially washed out more easily than the alkalines so the concentration of those is more noticeable than a salt pan like around the Great Salt Lake. An aunt and uncle moved to a place in one such area after selling their farm. Couldn’t even do a garden. My uncle considered this was a good thing. (It’s weird seeing on a satellite map these areas. They can be remarkably close to water and greenery. Using deliberate repeated flooding, some soils can be recovered but it’s costly and only works sometimes. You can see poor fields in the vicinity of that area.)

Is such stuff drinkable? It depends on the concentration and what else is in there. Metals can reach pretty bad levels in some. But metal poisoning from somewhat drinkable water doesn’t kill you very fast. But cattle and such are stupid and linger around water for a while so that’s bad.

If the concentration is high enough and the craziness from thirst is high, then a person can die from drinking the worst stuff in a matter of hours.