1. Preheat the oven to 425° F.

2. In a small mixing bowl combine the lemon zest, oregano, rosemary, garlic, and flour. Stir in the lemon juice to make a paste, then season with salt and pepper. Make ½-inch, deep slits allover the leg of lamb. Rub the lemon paste all over the leg, making sure it gets into the slits.

3. Put the lamb on a rack in a roasting pan and pour the water into the bottom of the pan. Roast the lamb 30 minutes. Reduce the heat to 325° F and continue roasting until a meat thermometer registers 145° F for medium-rare meat, 1 to 1¼ hours longer.

4. Transfer the lamb to a cutting board and let sit 10 minutes before carving. Skim the fat from the pan juices and spoon over the sliced lamb.