The words for water in various proto-languages are very similar
Water in 50 languages
The word for water in different European languages
"Water" in European languages
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So something I've noticed is almost all the proto-languages I can think of have their word for water (and stream/river, in the case of Korean and Sino-Tibetan) that starts with labial /w/ or /m/, or in some the words have /w/ as the second phoneme in the word.
Proto-Indo-European: wódr̥ / wed
Proto-Uralic: wete / witi
Proto-Malayo-Polynesian: wahiʀ / wahir
Proto-Sino-Tibetan: lwi(j) / m-t(w)əj-n / m-ti-s
Proto-Japonic: mentu
Proto-Tungusic: mū
Goguryeo: me
Proto-Mongolic: mören
Middle Korean: múl
Proto-Bantu: màjíjɪ̀
Proto-Afroasiatic: maʔ-
Proto-Eskimo: əməʁ
Proto-Chukotko-Kamchatkan: iməl
It's a strange coincidence, although I'm someone who likes finding genetic relations between language families so I like to imagine it's proof towards them being related ;)
All the ones that don't follow this rule that I can find are American languages. Some examples
Proto-Athabaskan: tuˑ
Dena'ina: tʰaʔ=naːn
I do notice they start with /t/ thought, which /t/ and /d/ appear as the first consonant of the first or second syllables of a lot of these words, which could also mean something
If you ask me, the words in PIE and Proto-Uralic are related, and the words in Korean/Proto-Japonic/Proto-Tungusic/Goguryeo/Proto-Mongolic are related.
Hindi: पानी (Paani)
Spanish: Agua
French: Eau
German: Wasser
Italian: Acqua
Chinese (Mandarin): 水 (Shuǐ)
Japanese: 水 (Mizu)
Russian: Вода (Voda)
Arabic: ماء (Māʾ)
Portuguese: Água
Bengali: জল (Jôl)
Korean: 물 (Mul)
Turkish: Su
Greek: Νερό (Neró)
Swahili: Maji
Tamil: நீர் (Nīr)
Urdu: پانی (Pani)
Dutch: Water
Hebrew: מים (Mayim)
Persian: آب (Āb)
Vietnamese: Nước
Thai: น้ำ (Nám)
Polish: Woda
Romanian: Apă
Czech: Voda
Hungarian: Víz
Finnish: Vesi
Swedish: Vatten
Norwegian: Vann
Danish: Vand
Indonesian: Air
Malay: Air
Filipino: Tubig
Ukrainian: Вода (Voda)
Serbian: Вода (Voda)
Croatian: Voda
Slovak: Voda
Bulgarian: Вода (Voda)
Malayalam: വെള്ളം (Vellam)
Kannada: ನೀರು (Neeru)
Telugu: నీరు (Neeru)
Marathi: पाणी (Paani)
Punjabi: ਪਾਣੀ (Paani)
Irish: Uisce
Scottish Gaelic: Uisge
Welsh: Dŵr
Lithuanian: Vanduo
Latvian: Ūdens
Icelandic: Vatn
Estonian: Vesi