1. People use it to rinse mouth, wash hands, pui pui phlegm, this is why hospitals use water dispensers (need to supply cups) instead of water coolers.
2. The water filter and pipes must be changed regularly, most don't. In some army camps, they out right remove the water filters, just use water coolers to provide cool and hot water.
3. Lastly, water coolers must be serviced regularly (hygiene). In addition, water supply must be tested for microbes at least quarterly, eg in hospital and army camps.