Hydrosphere.

[coco146 (OP)]

I'm terraforming a few planets with no access to water.  Does water have any affect and will adding water to the atmosphere have any effect on whether or not I have a hydrosphere?

[Nightstar]

AFAIK:

Hydrosphere affects planetary albedo. The only way it changes is if ice melts/freezes due to greenhouse terraforming, which can multiply the effects of said terraforming.

Water in atmosphere is useless beyond roleplay and being a generic gas.

[coco146 (OP)]

Thanks, so I don't need it then.

[Paul M]

Water is, or should be, a greenhouse gas.  So adding it is not a bad idea.  The other thing is that although in our overall atmosphere it is a relatively small fraction of the gas mix, in the region that matters to us humans it is around 4% of what we breath.

[IanD]

If Steve gets around to adding mobile asteroids perhaps he could add water ice asteroids, now that water ice has been discovered on asteroids. You could then "add" you water in one lump, preferably before the colonists arrive. The atmosphere could be a bit dusty for a while afterwards .