Mix water and lemon juice in a large bowl. Toss in pears and apples; let rest for 10 minutes. This will prevent discoloration. Drain fruits, discarding liquid, pat dry and return them to bowl. Add celery, carrots, walnuts and raisins. Toss with lime mayonnaise. Cover and refrigerate for 1 hour. Before serving, mix well and sprinkle top with mint and sunflower seeds.