The attempt to combine two liquids that do not normally mix with the aid of an "emulsifier" is known as an emulsion. Because hollandaise classifies in this category, it may take a few tries to get it right. Quite commonly, a hollandaise may "break," which means the two liquids separate, and your sauce becomes watery and alas, incorrect. To avoid this, the hollandaise must never get too hot, too cold, or have too much fat added at one time. To be safe, make your hollandaise right before you are about to serve it.
Don't get discouraged; practice makes perfect...and perfect eggs benedict!
Place the egg yolks and water in a bowl and whisk to combine. Place the bowl over a pot of simmering water on very low heat, creating a double-boiler. Make sure that the bottom of the bowl does not touch the water. Beat the yolk mixture over the heat for about 4 minutes, or until the mixture is thick enough that you can see the bottom of the bowl when whisking. Be very careful not to overheat your eggs, or they will cook (you may take the bowl off the heat from time to time while whisking). Remove the bowl from the heat and add the butter a little at a time, whisking well and placing back on the heat after each addition. When thickened to the right consistency, add the lemon, salt and pepper, and serve right away.