The best replacement for boiling water is steam.

The best alternatives to boiling water are rated as following:
★★★★★  steam
★★★★  humidifier
★★★★  microwave
★  cold air
  boiling oil
  filtering
  steam burn
  pressure canner
  simmering water

Your alternative for boiling water is not listed? Suggest!
Speaking about boiling water, one probably shouldn't forget about ice.

Other search terms related to boiling water and their ratings are:
★★★★★ ice
★★ vicks
You have in mind a companion for boiling water and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of boiling water in all years. Click on graph for more.
boiling water
steam
humidifier