Place sweet potatoes in a large saucepan with enough water to cover. Bring to a boil and cook 25 minutes, or until tender but firm. Drain, cool and cut into 1/2 inch slices.
Preheat oven to 350 degrees F. Lightly grease a large inch baking dish.
In a small saucepan over medium heat, melt butter, brown sugar, water and salt. When the sauce is bubbly and sugar is dissolved, pour over potatoes.
Bake in preheated oven for 1 hour, occasionally basting the sweet potatoes with the brown sugar sauce.