(Up one level to Eastern-Walu-Siwaish)
The PAN word for water was *daNum (Blust, ACD), *D2aNum (Tsuchida 1976), *daɫum (Wolff 2010). It is well attested all over Taiwan, including on the west coast (Saisiyat, Pazeh, Papora, Favorlang). It evolves regularly into PMP *danum. Barring special circumstances, this word should also evolve regularly into into Eastern Walu-Siwaish (EWS, north and east coasts). Indeed, among EWS languages,
- Basay (one dialect) lanom ‘water’,
- Trobiawan zanum ‘water’,
- Kavalan zanum (in qi-zanum ‘to drink’),
- Amis radom ‘carry water from the water source’,
- Paiwan zaɫum ‘water’,
show the expected outcomes.
However, equally widespread in EWS languages are forms reflecting PEWS *nanum:
- Basay nanom ‘water’,
- Kavalan nanum, m-nanum ‘to drink’,
- Sakizaya nanum ‘water’, mi-nanum ‘to drink’,
- Amis nanom ‘water’, mi-nanom ‘to drink water’,
- Puyuma nanum ‘water’ (male, religious),
- PWMP *ma-nanum ”pour water’
Perhaps *nanum referred specifically to drinking water while *daNum was a general term for ‘water’.
Papora mananu ‘to drink’ (Tsuchida 1982) is unrelated. The form contains man ‘eat, drink’ < *k<um>an, and –anu cannot reflect the PAN word for ‘water’: dom, dum, lom, rom in Papora.
In Kra-Dai, PAN medial *-N- evolves to *l, while *-n- evolves to *n. Compare *aNak ‘child’, Proto-Kra *lak, Proto-Tai *lɯ:k, Proto-Kam-Sui (Ferlus) *la:k 8; *buNum ‘air, weather, sky’, proto-Tai *C̬.lɯm A ‘wind’, Proto-Kam-Sui (Thurgood) *hlwɯm 1, (Ferlus) *(C)l/rəm A. Consequently, all the Kra-Dai words for ‘water’:
- Proto-Hlai (Ostapirat) *nam C,
- Proto-Tai *C̬.nam C (Pittayaporn; ‘C̬’ is a voiced consonant),
- Proto-Kam-Sui (Ferlus) *n-,
- Proto-Lakkja *num C (Theraphan)
are cognates of *nanum, not *daNum: *nanum has displaced *daNum in Kra-Dai.
Blust (ACD) treats the *nanum set as an unremarkable part of the *DaNum set. He overlooks the Amis doublet radom ‘carry water’ (from *daNum) vs. nanom ‘water’ (from *nanum), as well as the similar doublets in Kavalan (zanum/nanum) and Basay (lanom/nanom). He does however reconstruct PWMP *ma-nanum ‘pour water on’ which evidently involves a MP reflex of *nanum rather than of PMP *danum < PAN *daNum.
Interestingly, it appears that the PMP word *um-inum ‘to drink’ was reanalyzed from *mi-nanum ‘get water, drink water’ (here).
Reference
Tsuchida, S. (1982) A Comparative Vocabulary of Austronesian Languages of Sinicized Ethnic Groups in Taiwan, Part I: Western Taiwan. Memoirs of the Faculty of Letters, No. 7, University of Tokyo. Tokyo, Japan.