In 1-quart saucepan, mix water and lime juice. Sprinkle gelatin on lime juice mixture; let stand 1 minute. Heat over low heat, stirring constantly, until gelatin is dissolved. Cool slightly, about 2 minutes.
In medium bowl, beat cream cheese with electric mixer on medium speed until smooth. Add yogurt and lime juice mixture; beat on low speed until well blended.
Fold in whipped topping and lime peel. Pour into crust. Refrigerate until set, about 2 hours.