Agree, that’s a scary possibility! NICUs always use ready to feed formula, which is sterile. That’s a good option for babies under 3 months (after that age NEC is rare) or otherwise medically fragile, although it’s $$.
I think the other main option is to heat the water to a certain temperature that is hot enough to sterilize the powder but cool enough to avoid denaturing the proteins, mix, and then let the formula cool before giving to baby.
This is important to know even for parents who plan to breastfeed. I was a GE mom with a slightly premature baby and they wanted me supplementing her within like a couple hours of birth to avoid letting her sugars drop. (I was given a choice of RTF or donor breastmilk in the hospital, at home I used RTF until I was really confident about my milk supply.)
Hope that helps!