It simply can't get weaker by just sitting around. Only thing that might happen is slight fermentation, if you leave it for many hours unrefrigerated. Especially during warm weather. That is not dangerous, unless you leave it for several days and let the yeasts, plant sugars etc in the liquid to start really brewing. Even then, it might not be any more dangerous than unfinished, badly made home wine, but can be very bad for you if the pods had wrong kind of molds and/or yeasts in them. You can never be sure what kind of yeasts those pods have.