Bring water and rice to a boil in a saucepan. Reduce heat to medium-low, cover, and simmer until rice is tender and water has been absorbed, 20 to 25 minutes. Remove from heat and cool for a minimum of 4 hours or overnight.
Combine cooked and cooled rice, corn, imitation crab, eggs, onion, and cornichons in a bowl. Season with salt and pepper. Stir together mayonnaise and garlic in a small bowl; pour over salad. Mix well. Sprinkle with chopped dill.