To obviate something means to make it unnecessary by preventing it ahead of time or removing the need for it entirely. When you obviate a problem, you don't just solve it after it happens; you make it so the problem never comes up in the first place.

If you study your spelling words every night for a week, you obviate the need for last-minute cramming the night before the test. A good map obviates the risk of getting lost. When a school installs water fountains on every floor, it obviates students having to walk all the way to the cafeteria when they're thirsty.

The word often appears in the phrase “obviate the need for” something. Building a new bridge across the river might obviate the need for the old ferry service. Creating a clear schedule for chores obviates arguments about whose turn it is to take out the trash.

Obviate is about being smart and proactive. Instead of dealing with problems as they arise, you think ahead and arrange things so those problems simply don't happen. It's the difference between bringing an umbrella (which obviates the need to get soaked) and getting drenched and then drying off.