It would be hard to find something which is truly waterproof. My way of thinking is:
I don’t care.
What do I care about?
Is the manufacturer confident enough in the ability of their product to withstand water such that the manufacture will replace the device under warranty at no additional cost should the device suffer water damage.
If the answer is no then I am super careful not to get it wet. Such as the Dexcom Receiver. I am careful to not allow it to get wet even a little bit.
If the answer is yes such as with the Tandem t:slim X2 pump then I don’t worry in the slightest about water. For all practical considerations (which for us does NOT include scuba diving but DOES include Kayaking) we consider the Tandem to be waterproof. Tandem customer support has assured me they will replace the unit for any water damage and will not grill me regarding how long it was under water or how deep it went.
NOTE: Tandem support assumes the unit was not deliberately opened by the end user. The manual specifically states:
DO NOT open or attempt to repair your System. The System is a sealed device that should be opened and repaired only by Tandem Diabetes Care, Inc. Modification could result in a safety hazard. If your System seal is broken, the System is no longer watertight and the warranty is voided
In terms of what Tandem actually claims for their pump, Tandem states the pump is watertight to IPX7 specifications and further clarifies they specifically claim the pump is watertight to a depth of 3 feet for up to 30 minutes. The manual has further information on this topic if anybody is interested in the details.