Can you get hep c from drinking after someone who hasn’t been treated yet. Mistakenly drunk from someone’s flavored bottle of water, and didn’t know.?

ABSOLUTELY NOT. You are at zero risk of this happening. Hep C is transmitted via blood only so your blood needs to be in contact with the other person's blood. This is the same way HIV is transmitted, via shared needles or unsafe sex.
See https://www.cdc.gov/hepatitis/hcv/cfaq.htm.
No risk, no worry. The hepatitis C virus is not transmitted by saliva, shared eating untensils, shared drinks, etc. Only by blood exposure, as with shared drug injection equipment. (Even sex is pretty much an urban myth, with almost no sexual transmission except between men having traumatic rectal sex with othe rmen.) .