Combine water, vinegar and salt and cook in the top of a double boiler over hot water until liquid has been reduced to about 2/3 of the original quantity.
Beat the 5 egg yolks with the 1 teaspoon of cold water and add to the mixture. Beat well. Add the melted butter gradually, beating after each addition. Add the remaining 3 tablespoons of water, a few drops at a time.
Strain through a cheesecloth if you wish a fine-textured sauce.