In a medium saucepan, combine water, lemon juice, sugar and salt. Bring to a boil. Combine cornstarch and cold water until smooth; add to saucepan. Cook and stir over low heat until smooth and clear. , In a small bowl, beat egg whites until stiff peaks form. Add to saucepan and beat with a wire whisk until mixed, about 2 minutes. Let stand for 4 minutes. Remove from the heat and cool. , Meanwhile, in a small heavy saucepan, whisk egg yolks, sugar and salt until blended. Stir in milk. Cook over low heat until mixture is just thick enough to coat a metal spoon and a thermometer reads at least 160°, 6-8 minutes, stirring constantly but gently. Do not allow to boil. Immediately transfer to a bowl. , Place bowl in an ice-water bath for a few minutes, stirring occasionally. Stir in vanilla. Press plastic wrap onto surface of custard. Refrigerate until cold. , To serve, spoon pudding into individual serving dishes and top with sauce. Sauce will settle to bottom of dish. Refrigerate leftovers.