对 (duì) sounds to my ears more like /duei/. Similarly with 水 (shuǐ) /ʂuei/. Am I mishearing, or am I misunderstanding how Pinyin is supposed to be pronounced? Or is this a dialectal variant?
After [...] a consonant, iou, uei, and uen are simplified as iu, ui, and un, which do not represent the actual pronunciation.
This spelling seems to have been inherited from the earlier Latinxua Sin Wenz, itself following the use in Wade-Giles. Such simplifications were likely used since [wi] is an allophone of [wei]:
In SC [wi] is a variant of [wəi]... SC does not make use of such contrasts as [wi] vs. [wəi], or [ji] vs. [i], which English does (consider we vs. way, and yeast vs. east).
- A Phonology of Standard Chinese
Then we also have sounds that are there but simply left out, such as -ui actually being pronounced -uei (水, 对, 贵) and -iu actually being pronounced -iou (六，休，牛).
Most pronunciation you can find here. if not, try to searh the word you want to search +