Conventional wisdom is that people use about 100 gallons per day of water. My family averages less than 50, but maybe 100 GPD includes water use embedded in things we buy or use. About 350,000,000 people live in the USA. So adding the data on rainfall from this page, the Lower 48 receive about 100x the amount of water needed. That’s pure water desalinated and transported without any man made energy. Just need to be more efficient in collecting it.
That’s where rainwater harvesting comes in. Most every single-family home could collect enough water to meet the needs of the residents, especially when combined with graywater treatment and reuse. The technology is mature and reliable, and becoming more affordable every year. The process is specified in plumbing codes. The products are certified by independent third parties.
