Do they use the very same tomatoes and cheese? Those ingredients are key. If it's the water, perhaps they should try bottled water! I tried an Uno's pizza in Boston and it was a HUGE disappointment. Not even close to Chicago style. Not even close.
I talked to the owner of a West Palm Beach pizzeria. He said his stuff (flour, cheese, sause, etc.) comes from the same supplier he used in Brooklyn, NY. In Boca Raton, there's a restaurant with a micro-brewery. They filter their water and use it for beer and pizza dough. They're close, but no cigar.
So it's not what they're taking OUT of the water. It's whats MISSING from the water.
A note on British cuisine:
Dairy products in England are FAR SUPERIOR to anything served in the U.S. There is a much higher butterfat content. The butter, cream, etc. is FANTASTIC!
During our visit, we were treated every morning to "filter coffee." This is made in a French press gizmo. We bought one when we came home (we had to look around to find one that ISN'T made in France) and, when we're in the mood for a treat, we make a pot of "pressed" coffee.
Made with dark roast beans, it is AWSOME! Don't drink it after 7:00, though, or you'll be up well past 2:00!