I think the answer might be
A single breath, that's all I need to kill you,
Brething in water could kill you
Given properly, and I will refresh you.
If drunk, water is refreshing
Unable to avoid me, for life is what I provide,
Water covers 71% of the Earth's surface and is a major constituent of many living organisms
Always am around you, except where it's dried.
If there is not water it won't be wet, hence dry.
Now found on other planets!
Water is thought to exist as liquid beneath the surface of some planetary bodies.
Secret clue (thanks @Mohirl)
The initial letters of each line spells 'AGUA', the Spanish word for water.