In a 6-quart heavy saucepan bring wine and water to a boil with onion, carrot, celery, salt and pepper and simmer 20 minutes. Add oil and halibut and poach fish at a bare simmer, covered, until just cooked through, 5 to 6 minutes. Transfer fish with a slotted spoon to 8 plates. Spoon court bouillon over fish. Sprinkle fish with fresh coriander and garnish with lemon wedges.