Grate rinds of lemons with a grater or zester. Squeeze the lemons and strain out seeds; use all the lemon juice in recipe. Cream the butter and sugar thoroughly; add the eggs and mix well. Add the water, lemon juice and grated rind. Cook in top of double boiler until thick. Chill. Use this lemon butter as filling for eclairs, scones, or to serve with a plain cake such as angelfood or pound cake.