Can a 2 month old drink water?

My 4 yr old gave her sister half an ounce of water when I was in the restroom. Don't judge me but I have really bad hemorrhoids & stops me in my tracks when I feel a bowel movement coming so I left my 2 month old on her swing this time i didn't have time to grab her & take her with me so when I came back my 4 yr old was holding a bottle filled with water & said she filled it up herself from our drinking water & fed her. She still doesn't understand that shes strictly breastfed & watches other babies drink from bottles so she thought that's how she can soothe her sister while I was in the restroom

I feel so guilty & of course I can't be mad at my 4 yr old shes not a babysitter but I'm hoping the water doesn't cause anything. Anyone know if half an ounce can really harm an infant?

Shes not crying or showing amy signs of anything.