Access to at least the WHO minimum to meet basic needs is essential for health. This is one of the top priorities in disaster zones.
Without enough water, people cannot drink enough to avoid dehydration and its physical effects (which can include organ failure and death). People can't cook food or prepare formula for babies. People can't wash their hands and carry out personal hygiene activities to maintain their own health and prevent the spread of communicable diseases. Sewage systems won't work properly, toilets won't work, hygiene can't be maintained in places like hospitals and refugee shelters where it's really important for hygiene to be maintained. Disease then spreads among a physically frail, malnourished population. Operations can't be done safely. People starve and their organs fail. People die. Water is survival in disaster zones.
People might think "oh, but I only drink a couple of litres of water per day". It's not about purely what people have available for drinking. The majority of our essential water usage isn't what we drink.
The world needs to stop making excuses for this. If these figures were being reported about circumstances in a disaster zone somewhere like the USA or the UK, most people would be saying how awful it is and looking to see what is going to be done to ensure people get access to the WHO minimum at least, rather than saying "well, it sounds enough to drink to me". Another example of people's prejudices.