How to thin half and half to substitute for milk? I have a recipe that is for a "Texas-Style Blueberry Cobbler" (site is paywalled) from America's Test Kitchen. 

The recipe is as follows:


4 tbsp butter in four pieces + 8 tbsp melted &amp; cooled
1-1/2 c sugar (10-1/2 oz)
1-1/2 tsp grated lemon zest
1-1/2 c all-purpose flour (7-1/2 oz)
2-1/2 tsp baking powder
3/4 tsp salt
1-1/2 c milk


This makes a batter-style base (rather than the more traditional biscuit-style).

All we have on hand is half and half. In this usage, is it acceptable to replace the milk with some fraction of half and half cut with water?

This answer discusses something similar with cream.  I've found sites that say it's possible to do this but I'm not sure how trustworthy they are. Plus, they seem to disagree... some say to cut the half and half with water, other say to just replace it and expect a richer outcome.
Take out 4 tbsp butter and add the 1.75 c half and half.  That's what I'd do anyway.  It's about the same amount of fat and adds a bit more liquid back in.  Keep in mind that butter changes consistency depending on when it is put in or how it is applied, so it's possible this won't work so well if you have to do some whipping or something.
Do not add water.  You'll lose out on flavor.