With water temp you can probably use the Glycol incased probe although I am not sure if its been certified for use in liquids. I would avoid using the bare metal as it might not be IP rated for liquids and could short out.
https://meraki.cisco.com/product/sensors/sensors-accessories/glycol-encased-temperature-probe/
Someone from the MT product team would be best to answer this. Support might be helpful but given that not it's planned use they will probably say no.
With surface temp there isn't anything in the range that would accurately do this and depending on the temperatures you are monitoring might fall outside their operational range.
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