THC is nonpolar and only soluble in a nonpolar solvent such as an alcohol or lipid.
Water is a polar substance; hence, it's not going to have THC in it from your nasty dirty bong that you should be dumping out and cleaning regularly anyway.
Eww.
Besides, the cleaner your bong water, the less of a stain it will leave on the carpet when the inevitable spill happens!
