Melt the butter in a large pot over medium-low heat. Add the leeks; stir to coat. Stir in the water and salt. Cover the pot; reduce heat to low. Cook until the leeks are tender, stirring often, about 25 minutes. Uncover and cook to evaporate excess water, 2 to 3 minutes. Serve warm.
The LEEK CONFIT can be made 1 week ahead. Keep chilled. Rewarm before using.
