(to clickable tree)
In this post I argued that Proto-Eastern Walu-Siwaish (PEWS) innovated *nanum ‘water’, which competed with PAN *daNum. PEWS *nanum is reflected in all the EWS languages of Taiwan save Paiwan, as well as in all the Kra-Dai branches. A direct reflex is however not to be found in the Malayo-Poynesian languages, where *daNum reigns as ‘water’. In PEWS there existed a denominal verb *mi-nanum ‘to get water, to drink’: *mi-N constructions meaning ‘to acquire, get, obtain, collect, N’ are common Actor-Focus verbs in EWS languages. This *mi-nanum is the probable source of the main MP word for ‘to drink’: *inum, *um-inum.
Shortly before PMP, AF *mi-nanum ‘to drink’ underwent syncope of the unstressed middle vowel, much as in pre-MP *paŋudaN ‘pandanus’, giving Tagalog pandán, Malagasy fandrana, Malay pandan, Old Javanese paṇḍan, etc. This gave *mi-nnum. As the noun part of this *mi-N construction was not recognizable anymore, *mi-nnum was reanalyzed as*m-innum, with prefixed m- allomorph of <um> in words beginning in vowels. The internal cluster was then regularized, giving PMP *m-inum ‘to drink’.