This is a Forge mod that adds Hot Springs with Hot Spring Water.
Hot Spring Water is pretty much exactly like water, except it also gives entities the Regeneration effect and has some steam particles.
You can change the level and timer of the effect, and the effect itself, in the config. You can also prevent Hot Spring Water from making infinite water sources.
Hot Springs generate rarely on the surface in most Overworld biomes. By default, Hot Springs won't generate in biomes that are dry, sandy, savanna-like, or water-related (oceans, rivers, beaches). In the config, you can change what biomes are allowed, modify the generation rate, or stop Hot Springs from generating completely.
There are a few differences between the 1.12.2 version and the 1.16.5+ versions.
Check out Simply Hot Springs Wiki - Version Differences.
If you're on 1.12.2 and using Biomes O' Plenty, you also should check out Simply Hot Springs Wiki - Biomes O' Plenty Generation Info.