There are vast areas of fresh water flooded forests in Amazon River, Mekong River and Meghna River (Bangladesh) basins. In these flooded forests, the flora & fauna is richer than tropical ever green forests and many tree species grow more than 20 meters in height. These forests are inundated / submerged by river flood water up to ten meters depth for 5 to 7 months duration at a stretch. This paper avilable at following link explains how the flooded forest trees can be used for large scale water harvesting wherever water is available and needed.
https://docs.google.com/leaf?id=0B35UMaN-aVecNTQzMmE4MGQtMjFkMC00MTFhLWE5YzAtZjY5ZDczOTU5M2Vh&sort=name&layout=list&num=50