Keeping ducks is not always an obvious choice for a homestead or urban farm but they are extremely useful livestock to keep. They can produce as many eggs as chickens which surprise many people and the eggs are usually larger, fattier with large yolks, delicious. Ducks also are a good meat animal and the fat during cooking can later be stored for frying and roasting. From a self sufficiency angle I prefer duck breeds which are good for meat and egg production. Khaki Campbell’s are great for this dual purpose with the added bonus of being the best duck for eliminating the local slug population.
You do not have to have a pond to keep ducks but you should give the fresh water every day and give them somewhere at least to submerge themselves. In a perfect world they should have a water body of some sort, I lie to fill a large plastic pond with a screw plug at the bottom and refill it every month. The waste water makes good nutrient feed for the vegetable patch.
Overall I think ducks are a great addition to an urban farm or homestead. Children love them and they are fun to watch. I would say though especially to urban farming they can be quite noisy and will repeatedly quack late at night and early in the morning if you have close neighbours you will certainly here them in the night.
Starting a Duck Farm is a great book on the subject of raising ducks and farming various breeds.