I have 2012 Scion xd. I am experiencing a leak coming from under the dashboard.

Your drain line for the A/C has become clogged. Pull back the floor lining under the dashboard at the left hand side and you will see it leading from under the dash. Grab a plastic bag (I used a gallon size sandwich bag)and pull the line loose from under the dash. You may have to use some sort of tool (I used a very small precision screwdriver) to stick through the plastic tube from under the dash to clear the debris so you can get it to drain again. Once drained, reattach the rubber drain line. You will need to get a cabin air filter to prevent this from happening in the future. It installs behind the lower glove box. If it continues, it can short out the A/C fan. I learned that the hard way.