In large bowl, beat egg lightly; mix in bread crumbs, onion, parsley, horseradish, water, mustard, salt and pepper.
Mix in beef; shape into 4 patties, about 3/4 inch (2 cm) thick.
Grill on greased grill or in grill basket over medium-hot coals or at medium-high setting for 7 minutes.
Turn and grill for 7 to 10 minutes longer or until no longer pink inside.
Serve on English muffins.