In a food processor, pulse the egg yolks, lemon juice, ground mustard, real salt, garlic powder, and onion powder until just barely combined.
Melt the butter and coconut oil until just barely melted (don't allow to get too hot lest it turn the egg yolks into scrambled eggs).
SLOWLY drizzle the butter-oil mixture into the food processor as it is running. Be sure you gradually pour it in as a drip or a very tiny drizzle to ensure that the mayonnaise properly emulsifies (emulsification is where the egg yolk and oil mix without separating).
Slowly pour in the water until mixed.
The mixture should thicken as it emulsifies and again as it cools (especially in the fridge). If it becomes too thick for your taste, thin it down with more warm water, adding one additional teaspoon at a time until it is has reached the preferred consistency.
Store in the fridge. Should last about 2 or 3 weeks (if it starts sprouting green or black stuff, I'd throw it out....).