- Rain water collected in ponds/rivers may be contaminated/infested.
- Lack of fresh water in the ocean/islands is also an issue.
The two things that are available almost everywhere are air and sun.
It's reasonable to condense drinking/cooking water from air with solar energy in places that lack secure water. Not water for other purposes; you can't run a cooling tower, irrigate a field or an orchard, water a herd of cattle, or even grow a garden that way. But a household-sized dehumidifier powered by a household-sized solar panel can certainly make enough water to drink and cook rice.
On the other hand, if you live in semi-arid desert or any wetter biome, a cistern probably has a better cost-benefit ratio. Depending on your aquifer, a well may be better still.