In a bowl on top of a saucepan of simmering water, whisk the lemon juice with the water and egg yolks until thick and fluffy.
Remove the bowl from the double boiler. Off the heat, drizzle in the butter, whisking constantly. Season with salt and pepper. Keep aside at room temperature. Reheat on top of the double boiler, over simmering water whisking just for a few seconds, just before serving.
Serve the sauce with salmon coulibiac or with fish, vegetables or egg dishes like eggs Benedict.