Undergraduate / 'experience in Venice' - An experience that has changed your life [7]

Avoid using passive voice. "In between rustic houses and buildings run narrow waterways which flow to the Grand Canal" is a good example. Instead, phrase it something like, "Narrow waterways run between rustic houses and buildings, flowing down into the Grand Canal."

In addition, like EF_Kevin said, description is good, but this essay is supposed to be about you and how these experiences have affected you.

Undergraduate / Basketball has become an indispensable part of my life - Common app short essay [7]

Grammatically, your essay has several problems: Keep your tenses consistent, and watch out for those runons and sentence fragments.