You know SoilMoist, those polymer hydrogel granules:
http://www.soilmoist.com/soilhome.html

If you're interested, the NY Times had a related article:
http://nytimes.com/2004/07/20/scienc...G8m+5qAo52Xhow

Say I mixed Soilmoist with topsoil for my lawn. Does anyone know how
long this stuff will last? I have no idea. For all I know it could
last forever, but I doubt it.

Thanks for your help.