In Revelation 8:10-11, it says:
And the third angel sounded, and there fell a great star from heaven, burning as it were a lamp, and it fell upon the third part of the rivers, and upon the fountains of waters;
And the name of the star is called Wormwood: and the third part of the waters became wormwood; and many men died of the waters, because they were made bitter.
We have argued that global warming will serve to bring about a number of prophecies found in Revelation. Global warming will rapidly accelerate after the Arctic becomes ice-free during the summer months, as it will unleash a massive explosion of methane into the atmosphere. The rising atmospheric temperature will also cause the water temperature in lakes and streams to similarly rise. Toxic algae blooms will then occur, poisoning our drinking water.
What is currently happening in Salem, Oregon is representative of this argument.
Toxic algae blooms are occurring in local sources of fresh water used to supply drinking water. People are now unable to drink water from the tap. Though these isolated cases are still uncommon, we hold that as temperatures spike, so will these instances increase.
Only those who have enough land to harvest rain water and store it in tanks will be able to have a practical way to deal with this issue once the Seventh Seal is opened. Perhaps those with the means should prepare to help serve their local community when drinking water becomes a scarce commodity.