As we know, according to IATA passengers allowed to carry no more than 100 ml of liquids on board. Yet when traveling with low-cost airlines, you are not offered any water on board. This is quite harmful, considering the dry air in the cabin. Being used to my country laws and social norms that allow anybody to ask for a free glass of water in any place that serves food, it sounds strange that I don't seem have the official right to ask for a glass of drinking water during the flight. Are there any IATA regulations or subject, or is it based purely on airline good will decision?
The IATA best practices guide (http://www.iata.org/publications/Documents/cabin-operations-safety-bp-guide-2015.pdf) has only rules about serving alcohol to passengers. So it is safe to assume, that there is no other IATA rule regarding drink service. When it comes to laws, each law would be country specific. At least Germany doesn't have such a law, which would require airlines to provide free water.