Glass Bottle

The Glass Bottle is an item that was added in 1.9 Pre-release 2. It is possible to pick up Water with bottles to make Water Bottles, which are a vital part of Brewing.

Usage
Glass bottles can be used to make Water Bottles. and making Potions bottles

Bottles may only be filled by using a water source block or a filled Cauldron. If filled via water source, the water will be unaffected. If filled via cauldron, however, 1/3 of the water in the cauldron will be removed. Therefore, using a Cauldron to fill bottles is inefficient, except in the Nether where it is the only way to fill bottles or if there is no water nearby.

You can also drink the water, which doesn't have any effect on you but empties the bottle.

History
The Glass Bottle was first added in Beta 1.9 Pre-Release 2. They were given their sole function of picking up Water for Potions in Beta 1.9 Pre-Release 3.