The download button opens the iTunes App Store, where you
may continue the download process. You must have iTunes installed with an
active iTunes account in order to download and install the software. This
download may not be available in some countries.
From Mothership Software Limited:
WaterIn is a simple App to help remind you to drink water. There are many opinions about how much you should drink, that's up to you to decide. For example if it's hotter then you should probably drink more.