Fill a medium sized saucepan with two inches of water and bring to just about a low simmer. Maintain this heat throughout the cooking process. Take a heat proof bowl (Pyrex or a stainless steel mixing bowl) that fits on top of the saucepan without touching the water, and add the egg yolks and water. Whisk the mixture over the double boiler until the liquid is frothy, thick and has doubled in size (3-5 minutes). You should be able to make a "ribbon" out of the mixture when you lift the whisk out of the bowl.
Slowly add a cube of butter (one piece at a time). Whisk until the piece of butter is completely melted and then add another cube. It is very important to add the butter to the eggs slowly, and to whisk continuously.
The sauce will begin to look a little thinner as all the butter is added, but keep whisking, it will thicken up after 10-12 minutes (from the start of the butter additions to the end of cooking).
Once the eggs have reached the correct viscosity, remove from the heat and place on a rack or trivet. Whisk in the salt, pepper, and lemon juice. Allow to cool slightly for 5 minutes before using.