In a large bowl combine flour, salt and sugar. Cut shortening into flour mixture. Mix together water, egg and vinegar. Add to flour/shortening mixture, mix together and form into a smooth ball, but don't over-mix. Chill 15 minutes. Divide into 4 balls.
Makes enough dough for 2 large double-crust pies, or 5 single crust pies. Dough can be frozen.