Bring water to a boil and add in pasta. Add a little bit of salt to the water. Mix every once in a while to make sure pasta doesn't stick to the bottom of the pan. Make sure you watch the pan so the water doesn't boil over, salt will cause the water to bubble more.
Chop onions and celery and add it to the mixing bowl.
Add in mayonnaise, garlic powder, parsley, salt and pepper.
When pasta is done boiling, strain the pasta and add the pasta to the bowl.
Mix well using a large spoon or rubber spatula.
Cover and place in the fridge. Let the pasta salad cool for about 2 hours before serving.
Before serving, add more mayonnaise if necessary. The pasta will soak up some of the mayonnaise and you might need to add more. Usually you can see if the salad looks too dry.
Notes
Store covered in the fridge. Save for up to one week.