Trust me on this: don't drink that water.
Even if it costs a fiver a day in bottled water, don't go anywhere near those machines.
Under the Workplace (Health, Safety and Welfare) Regulation 1992, the employer has a responsibility to provide an adequate supply of drinking water. However, the employer must ensure that the facilities provided are done so safely and are maintained correctly to avoid any risk to the employees.
If those water machines are unhygienic, then Ryanair are in breach of current legislation and are breaking the law.