Preheat the oven to 450F. Line 2 baking sheets with parchment paper.
Add water, butter, sugar and salt to a saucepan and bring to simmer. Once it starts simmering, remove from heat, add flour and stir right away until the mixture turns into a dough ball. Let stand for 5 minutes.
Add the eggs to dough one at a time and mix until incorporated into the dough.
Put dough in a pastry bag with a large tip and pipe small rounds of dough on baking sheets, spacing 2 inches apart (it should make about 20 pieces).
Bake cream puffs for 10 minutes at 450F, then lower the temperature to 350F and bake for 15 more minutes. Remove the puffs from the oven and let cool completely.
While the puffs cool, make the filling. Put heavy cream with a bowl and whip with a mixer until thick. Add powdered sugar and mix until combined.
Split each cream puff in half using serrated knife and put a scoop of whipped cream inside the bottom half, then put the top half back. Sprinkle with more powdered sugar if desired.