As Water is the basis for life, it seems to me that "The Greatest Invention" would pertain to water supply. Therefore, I nominate "Airwells".
I have compiled a comprehensive collection of articles & patents, &c on the subject. They are available at
rexresearch[.]com/airwells/airwells.htm
rexresearch[.]com/airwell2a/adsorbairwl.htm
rexresearch[.]com/airwell2/airwell2.htm
rexresearch[.]com/airwell3/airwell3.htm
rexresearch[.]com/dewpond/dewpond.htm
rexresearch[.]com/ellsworth/ellsworth.htm
rexresearch[.]com/hoffwtrbox/hoffwtrbx.htm
rexresearch[.]com/airwells/klaphake.htm
rexresearch[.]com/kohavi/kohavi.htm
rexresearch[.]com/parent/parent.htm
rexresearch[.]com/theilow/theilow.htm