Can you water down half-and-half milk with water to make 4% milk?

Not precisely. There’s more to milk than fat. You’d just have watery half and half.

You could add half and half in small quantities to other milks, however, which would increase the fat content without diluting the other milk contents.

Your perfect fat level is up to you. At some point of fattiness, the texture alone puts a lot of people off, but chefs have repeated for generations, “fat is flavor”

Try it with a small amount and see what happens. You might also try mixing skim milk and half and half.

Why not just buy whole milk?

@janbb I buy 3% milk. I was just wondering what 4% milk tastes like.

Try mixing with skim milk, rather than with water. Lower fat milk is MILK with less fat, not milk with water added.

And if you want to actually understand what you’re dealing with, try searching for “milk versus half-and-half” and reading articles about it. It’s not just a spectrum of milk with different levels of one type of fat in them.

See for example:
https://www.livestrong.com/article/531735-nutrition-information-of-milk-vs-half-and-half/

I sometimes put water in whole milk for cereal when I’m at a hotel that doesn’t have skim. It doesn’t taste the same, but it passes with cereal. I probably get it down to 2%.

Half and half will probably even be more difficult to get it to taste like regular lower fat milk. Maybe because it’s not homogenized all together.