Why can't I pour water out of the pitcher right after filling it?
Edited
After filling the pitcher, the water takes a few minutes to filter into the lower tank before the pitcher is poured. This ensure's the water is thoroughly filtered prior to you drinking it.
If you pour water from the pitcher while water is still in the upper tank, two things may happen:
Non-filtered water will likely enter your cup as water will escape via the gaps around the lid.
The lid could pop off if you do not hold the lid as you pour.