We know from GtG and KoS is that with the Windstop Orlanth and Ernalda are dead. Immediately a Great Winter began and everything froze. The air is dead, the winds are gone. "Children were not born, seeds did not sprout, fruit did not grow" and "All of Kerofinela froze".
What I'm wondering about is other effects.
1) The rivers of Dragon Pass. No winds, no clouds, no rain. And freezing air. That suggests that most rivers in Dragon Pass dry up and/or freeze over except those protected by the Moon (i.e. the Oslir and the Black Eel - and even those would substantially diminish as their headwaters would still dry/freeze up). The Malthin, Lyksos, Marzeel, Bullflood, and Minthus are all affected this way and most of the Gorphing. Some tributaries of the Gorphing extend farther into Maniria outside the Windstop. They might get some wind/rain by the air/storms sucked towards the Windstop, but my thought is that those waters freeze over or are sucked into the dead earth as they pass the Windstop. Does that make sense? And what of the River of Cradles?
2) The Upland Marsh. Presumably Delecti can fend off the effects of the Windstop in his 'dead' waters? This would mean that 'some' water can be found by desperate Sartarites attracted to the open water. At the same time, this could just be a lure by Delecti to boost his undead population (and the undead may roam farther to seek the dying and bring them to the Marsh for 'conversion'). It may also mean that the Ducks have a greater chance of survival because they can get water and harvest weeds or grains from the Marsh, and some folk might shelter in Duck Point (if not occupied still by the Lunars) as one way to survive the Great Winter.
3) Choralinthor Bay and the Syphon River. Fed by the oceans, the Choralinthor does not diminish, but may become saltier without the flow of fresh waters into it? Does/could it freeze over? My guess is not, except near the land margins (the Rightarm Islands may suffer freezing when the tides drop, then the ice melts as the tide rises). The Syphon, running backwards, would still flow at the start and likely still flows up into the print. But it would be entirely salty now and everything along its banks would be contaminated by salts, as well as freezing.
4) The Skyfall. What happens here? This is a hole into the Gods World/Gods War. I'm thinking that the hole might in fact expand and the entire area over the Skyfall Lake would be inundated by the waterfall. But the clouds that normally shroud the Skyfall are gone. That would mean that the trolls have water, and the water of the River would still flow down into Snakepipe Hollow. I could see that the Dwarf might employ his tools to keep the River moving past Dwarf Run, and perhaps it has enough flow beneath the ice over it to reach the Upland Marsh. Again, desperate folk might seek to reach the River, and even brave the horrors of Snakepipe Hollow to get water.
5) The River. Assuming the Skyfall still pours down and the River still has current beneath the ice at least to the Upland Marsh, does any water still flow on south past the Marsh? Perhaps enough to reach Duck Point or the Wild Temple, I'd guess, but it would freeze over and dry up somewhere after that. It would not make it to the junction with the Lyksos or Choralinthor Bay without the added volume of rain and tributaries such as the Creek and the Stream.
And what does that mean for the folk under the Windstop in terms of getting water?
1) Melting ice. Fire (or Moon) magics are critical to melt what ice there is and draw water from that. This may work at the start, but is increasingly difficult in Dragon Pass after the first season (except perhaps for glaciers/snow on the mountain peaks). Probably still effective in areas like along the River or maybe in Caladraland (if water sources are found).
2) Summon water from within the earth. Shaman and dwarfs (and maybe River or Moon priests or Earth Witches) can summon waters up from within the dead/sleeping earth. May require a lot of dowsing/divining or seeking through the spirit world to find such sources. These could be anywhere - under the Quivin Mountains, within the Dragonspine, by Dwarf Run and the Vent (I'm sure the Mostali have good water sources hidden away), under the Delainan Hills of Esrolia, perhaps under the Grazelands or Beast Valley. The Grazelanders, Beastfolk, and Telmori may have the advantage of sufficient shamans to perform these rituals and draw the water up (particularly since Ernalda is dead and the earth goddesses sleep).
3) Purifying Bay or Upland Marsh water. River and Choralinthor priests (maybe shaman) can use their magics to purify the waters of the bay or marshes of salts/poisons and make it drinkable. This means that the cities by the Bay suffer the least - Nochet, Rhigos, Storos, Karse, Sklar, Backford, Leskos, maybe Durengard and Vizel.
4) Departing for those areas where there are known water sources. If they can make it there and aren't targeted as food along the way or at the destination by trolls, Telmori, chaos and undead.
Other thoughts? And what can the Moon priestesses do to help ameliorate this suffering (and get converts in the process)?