Rules Guy: What happens if I lose the ball I just marked?

After marking ball on green and picking up ball, golfer or caddie drops ball, which rolls into water hazard, not retrievable. Replacement ball of exact brand and kind not available. What is penalty and how to continue?
—EARL HUSBAND, ODESSA, TEXAS

Ball lifted from putting green must be replaced. Must be exact ball. If not same ball, make/model no matter—substituting ball without authority under Rules. Two strokes or loss of hole is penalty. Also, One Ball Condition of Competition only encouraged for pros. Top-tier amateurs, too. Not for club play. Suggest: Grip ball tight!

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