Combine water and 1 tablespoon lemon juice. Working with one artichoke at a time, bend back outer green leaves of artichokes, snapping at base, until reaching light green leaves. Trim about 1 inch from top of artichoke. Cut off stem of artichoke to within 1 inch of base; peel stem. Cut artichoke in half vertically. Rub edges with cut lemon, and place artichoke halves in lemon water. Repeat with remaining artichokes. Steam artichoke halves for 12 minutes or until tender.
Combine yogurt and next 6 ingredients (through pepper). Serve artichoke halves with dip; garnish with dill sprigs, if desired.