JerryRigEverything went all out on the OnePlus 6 and one of the things he specifically wanted to find out was how waterproof is the phone. OnePlus when launching the phone, did not mention any IP certification for the phone, but what JerryRigEverything found out was rather surprising.
iFixit gave the phone a 5 over 10 score mainly because of the strong adhesive under the glass back which certainly will help against medium water contact. Other than that, JerryRigEverything also found out that there is waterproofing rubber around the headphone jack and USB port, alongside water-resistant meshes protecting the speakers and mics. However, the SIM tray did not have very good water-proofing which could be a potential point-of-failure if it comes into contact with water.
Based on his finding, JerryRigEverything has concluded that the phone has the same amount of waterproofing as an IP67 phone, which is pretty decent. However, that does not mean you can throw your OnePlu 6 into the swimming pool, as OnePlus did not register the phone for an IP certification. It will probably be fine to take the phone out when it is raining, but best not to push it further than that.