I agree both with Todd's arguments and with the rest of the answers, so I'll try to wrap it all in a way that makes sense.
Technically, water is challenging and requires lots of resources. It has a lot of gameplay potential, which is good, but it's also the cause of its cost. That's why I think that "water-related-stuff" shouldn't be developed before launch.
On the other hand, some parcels just doesn't look good enough without water. And that's why I think that simple, non-functional, water should be ingame before launch. Ankle-deep, suffocating state,... Anything would do.
There are a lot of long term possibilities that could be explored in the future and some are far less "expensive" than others. A move speed debuf on shallow water, a speed buf when moving downstream, caravan-rafts, plants/trees/mobs that appear only near water, toxic/polluted/poisoned waters, frozen lakes, floodable areas reacting to rains, mills and buildings benefiting from being next to rivers, artificial water channels for farming purposes,...