Line a 9-inch square pan with aluminum foil, leaving excess foil hanging over edges. Grease foil liberally with butter. Arrange pretzels and pecans on bottom of pan.

Combine caramels and water in large saucepan over medium-low heat. Melt, stirring, until smooth. Pour over pretzels and pecans.

Melt butter and chocolate together in a large bowl set over a pot of simmering water. Spread over caramel. Let sit at room temperature until cooled, then transfer to refrigerator to set.

To remove candy from pan, use edges of aluminum foil to lift out of pan. Peel off foil and transfer candy to greased parchment paper. Use a buttered knife to cut into squares.