The best way to estimate the basin water catchment area in a particular area is a technology of remote sensing and geographic information systems implementing digital elevation model (DEM) .
I'm not familiar with U6 snRNA, however it definitely seems like DNA contamination. A few things could be introducing DNA in addition to your water and RNA template. Mastermix? Primers? Even pipettes or tips.
I am just wondering if you resolved your issue? I am also having this problem. I am using the U6 Taqman assay from Thermo and have tried new water, new kits, new assays and still get amplification in my no RT control.