I think (from posts in other threads) OP only visited Hong Kong, where drinking water and hygiene standards are very high and have been for a long time, dating back to the British colonial period. Their tap water is actually some of the best in the world.

Not to say it couldnt be possible - many ingredients come from elsewhere in the region - but HK operates under a totally different set of public health and hygiene standards and is much less of a likely culprit than the rest of the PRC.