Preheat the oven to 400 degrees F. Line two baking sheets with parchment paper and set aside.
In a medium size sauce pot, add the water, butter and salt and place over medium heat. Stir occasionally until the butter has melted. Remove from the heat and add the flour. Using a wooden spoon, quickly mix until well incorporated.
Place the mixture back over medium heat and cook, stirring vigorously until the mixture begins to pull away from the sides of the pan and form a ball, about 2-3 minutes. Continue to cook, stirring, until the dough dries out somewhat and no longer looks as pale and sticky (instead looking more shiny), about 2-3 more minutes. Note, you should also begin to see a slight film on the bottom and sides of the pan, this is an indication that the dough is cooked. Remove the pan from the heat and cool slightly.
Once the dough has cooled for a few minutes, add the eggs, one at a time and mixing thoroughly in between. Mix in the Gruyère.
Place the dough in a pastry bag fitted with a 1/2″ pastry tip. If you do not have a pastry bag, I suggested using a large ziplock bag instead, just cut one of the corners and insert the pastry tip.
Pipe 1-inch rounds about 2-inches apart onto the prepared baking sheets.
Using a pastry brush, lightly brush the gougéres with the egg wash. Sprinkle generously with poppy seeds.
Bake the gougéres until puffed and golden, about 20-22 minutes. You will know the gougéres are done when you tap them and they have a slightly hollow sound.
Serve warm. Note, for dinner parties you can also make the dough a few hours prior to baking off, if prefered. You can also bake the gougéres and reheat them right before serving if needed.