Tornillo Creek sometimes looks like it is covered in snow because of all the white calcite-salts precipitating out of the water as it evaporates. The water is at full saturation with calcium carbonate and water filters will not remove it. The water will have a limey-taste to it even when filtered but is potable. If you drank it every day it would probably give you kidney stones but for a day or two it's fine. I have drank it several times with no ill effects but would still recommend avoiding it if possible.
I think the rangers now use some sort of dry-erase board to write spring reports on but most of their information seems to pertain mainly to well known and often visited springs (Mule Ears, Fresno, Boot). TWWG