Not just drowning victims. Many freshly dead persons will have Dihydrogen Monoxide in their system, including but not limited to their lungs. They try to keep it a secret. Doctors will usually not write it down outside of the mentioned drowning.
If the body decays, that's a strong sign the person had the substance inside it at the time of death.
Big dihydrogen monoxide. Private dihydrogen monoxide companies made approx. $303 billion globally in 2022. This number doesn't include governments selling this stuff too. No one tells you that on the low end this stuff kills 300,000 + people a year globally. Look-up in Google "HOH chemical", and you'll learn everything you need to know about dihydrogen monoxide.