Put one inch of water in a large saucepan over medium heat and bring to a simmer. Once simmering, reduce heat to low.
Place egg yolks and water in a medium mixing bowl and whisk until mixture lightens in color, 1 to 2 minutes. Add the sugar and whisk for another 30 seconds.
Place the mixture over the simmering water and whisk constantly until there is a clear line drawn in the mixture when you pull your whisk through, or the mixture coats the back of a spoon, 3 to 5 minutes.
Remove the bowl from the pan and gradually add the butter, 1 piece at a time, whisking until all of the butter is incorporated. Place the bowl back over the simmering water occasionally so that it will be warm enough the melt the butter. Add the salt, lemon juice, and cayenne pepper. Serve immediately or hold in a thermos to keep warm.