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When water is poured out in space, why does it always take a spherical ball-like shape?

Minimizing energy. If there is a small amount of water, then surface tension wants to try and minimize the surface area of it, and the minimum surface area for a given volume material is a sphere. For really large volumes of water (if you, for instance, sucked all the water out of the oceans and placed it somewhere far away in space in the standard mad-scientist way), then you also get a sphere, but for a different reason: the mass of water wants to minimize its (self-)gravitational potential energy and this is also done when it is spherical. If such a volume is in the presence of external gravitational field (for instance if it was orbiting the Earth) then it would not be completely spherical: this is one of the reasons the Moon has a slightly odd shape, for instance.

In between these two regimes -- if you had a few thousand gallons of water for instance, then although it would eventually end up spherical in the absence of other influences, this would take a very long time.

No, it's not because of gravity. You need to take quite a lot of water in order for gravitational effects to become significant.

It's because of surface tension. Sphere is a shape which minimizes the surface for a given volume. The surface-tension-related potential energy of the water is proportional to the surface, so spherical shape minimizes the potential energy.

I’m sure that a chemist could give a deeper answer. Or from Wikipedia we get, the surface tension occurs because water has hydrogen bonding.

Because of its polarity, a molecule of water in the liquid or solid state can form up to four hydrogen bonds with neighboring molecules. These bonds are the cause of water's high surface tension and capillary forces.

The key are the 4 possible hydrogen bonds to other water molecules of liquid water. The water molecules are bonded to each other like a free dimensional mesh.

Heating water, the water could be sprayed out in space to small pieces of course. The hydrogen bonds are weak (compared to metallic bonds) and under the influence of heat transfer the kinetic energy of the water molecules increases and the hydrogen bonds get broken.

Thanks for adding the the H bond piece. When H2O is discussed the H bonds need always discussed. For the previous answers... well, good stuff yes. Aside from the pragmatic human behavior implications of molecules. They don't have a choice, period.