Combine the water, milk, butter, salt and sugar in a saucepan and place over low heat until the butter is melted.
Once the butter is melted completely, turn the heat on high and bring to a boil.
The moment it comes to a boil, remove off heat and immediately add the flour, all at once. Mix well with a wooden spoon or spatula until the flour is well absorbed. Place the saucepan back over medium flame and continue cooking for 2-3 minutes, mixing all the time, until a layer of dough remains on the bottom of the pan - keep the flame on medium to avoid burning and mix all the time with the spatula or spoon to cook out the liquid.
Remove from heat and allow the dough to cool down for 10 minutes.
Start incorporating the eggs, one by one, mixing well after each addition. Add the last egg bit by bit to make sure you're not adding too much egg. The number of eggs used depends on the humidity of the dough, even on weather and the size of the eggs.
The dough is ready when it falls off the spoon and leaves a streak that doesn't collapse on itself if you run your finger through it.
Spoon the dough in a pastry bag fitted with a star nozzle and pipe small and even eclairs on a baking pan lined with baking paper or a silicone mat.
Bake in the preheated oven at 350F for 40-50 minutes, depending on the size of your eclairs.
The eclairs are done when they are golden brown and crusty. Place aside until needed.