Hello!
It's best to make a tea from fresh seeds (not dried).
Tea made from dry seeds are too hard on healthy kidneys and could be toxic to weak kidneys.
When seeds dry they get into a 'dormant' state, and convert most of their 'live' energy into 'reserve energy' to be used -as fuel- when germinating.
Warning:
Many dry seeds are not for human consumption, but for growing new plants from them.
They is no guaranty they are free of pesticides, preservatives , microorganisms, molds, or any other contaminant.
Just cut open a fresh, ripe watermelon, and pluck the seeds out;
grind them and brew
Enjoy!!