Pasta water substitute? If you aren’t making pasta, what would you use as a pasta water substitute?

I would use regular water as a substitute.

The reserved pasta water is used to thin the sauce after you mix in the pasta. Pasta tends to absorb liquid, which would make the sauce thick and more difficult to coat the pasta well. Since you are evidently not going to serve this with pasta, the sauce shouldn't need to be thinned out any. However, should you find this necessary you can add a 1/4 teaspoon each of salt and cornstarch to 1 cup of water, microwave that for a minute or two until it's hot- and then use that as a substitute for pasta water. This is what American's Test Kitchen says, at least.