My idea is to combine the designs of the Brita pitchers and Brita bottle to create a hybrid bottle/pitcher.  The Brita bottle is nice since it is portable and you can drink directly from the container.  However, I like that the pitcher filters the water when it enters the container rather than when it leaves the container as occurs with the bottle.  Also, the pull-up lid on the bottle can wear out over time and some days the bottle isn't big enough. 

First, the bottle/pitcher would have two openings.  One opening to fill the bottle with unfiltered water, and a second opening that you can drink out of or pour into a cup.  There would be a chamber in the bottle similar to the current Brita pitchers where the water is filtered.  This way, you have filtered water available rather than filtering it each time you drink out of the bottle.  The one-liter bottles are very popular and a great size to keep at your desk at work, so that would probably be a good size for the bottle/pitcher.