Lay out the phyllo pastry sheets on a counter. Cut them into 16 identical squares, without separating them out.
Smear them with butter. Beat the eggs. To them add the crumbled feta cheese and a little oil. Stir well and distribute the mixture onto the squares.
Carefully fold each square to make it into a triangle. Arrange the phyllo pastries tightly in a buttered oven dish.
In a bowl, beat the mayonnaise with the water. Pour it over the phyllo pastries and bake at 392°F (200 °C) for 15-20 min.
Leave them to cool a bit and then serve.