In my experience, whenever I've asked for a Cafe Americano, the restaurant has served this in a normal size cup and added the hot water already. I've never had hot water served "on the side".
A similar drink is Cafe Lungo ("long") which uses an espresso machine to make a single or double shot of espresso with more water.
A few other points for your husband to note.....
Coffee is generally ordered and paid for at the Bar, and then the receipt is given to the person that actually makes the coffee.
Coffee is generally consumed at a neighborhood Bar (the word "Bar" in Italy has a different meaning than we're used to). Pastries, Sandwiches and other items are sold also, as well as liquor.
If he orders "un cafe" (which is what most Italians order), he'll probably get espresso in a demitasse cup.
Italians don't usually drink Capuccino after about 11:00 or so (but there are always exceptions).
Also note that he'll pay for EVERY cup. It's rare to find free refills, except during breakfast at B&B's or Hotels.
Seating at the Bar is generally cheaper, while seating at sidewalk tables usually costs more.
Cafe Americano doesn't quite "taste" the same as normal drip coffee, but it's the most similar so he'll have to tolerate the difference during the trip.
If your husband wants to be "adventurous", he might try Cafe Corretto, ("corrected") which has a shot of Grappa (or other liqueur) added to the coffee!
Cheers!