You might be looking at the next global crisis right now.

Because as easily as most people get a clean drink out of the tap, billions of people can't take that for granted. This problem is only going to get worse.

For decades water access has been a slow-growing crisis as many parts of the world struggle to secure clean, reliable supplies. Today, out of the world's 500 largest cities, approximately one-in-four can't always meet their own needs. In 20 years, according to United Nations estimates, global demand will exceed the supply by 40%.

Twenty years from then at least a quarter of the world's population will live with chronic or recurring shortages.

Yet where residents of California may live this as a fight over who gets a green lawn, in poor and developing regions this can define an entire way of life.

"Water access is about freedom to be fully human," said Pierre Ferrari, President and CEO of Heifer International. "It's impacts are staggering for farmers in our programs. Water is fundamental to their economic stability, as they depend on it for irrigation, livestock watering and feeding. But the psychological impact of not having clean water is also immense — we see anxiety, fear and depression in communities that lack access."

"In our work in arid areas, the daily search and transportation of water for drinking, hygiene and cooking is constant and overwhelming. It is a main use of energy by all, but mostly a task that falls to women and girls. Making clean water easily accessible may be the single most important intervention to give women and girls the freedom to escape poverty and oppression. All these can be lifted as water becomes available." 

Water is definitional. Health, safety, food, it all starts with access to a clean supply, and communities will redefine their entire identity around finding and securing that access. As Ferrari notes, everyone and everything is influenced when that supply is disrupted.

Perhaps the most critical loss of all is time. For people who can ill-afford more uncertainty and disruption to an already-fragile standard of living, getting water can demand hours of time that they simply can't spare.

In developing communities across Africa and South Asia, usually it's women who average a half an hour getting each and every bucket of water. Worldwide, women and girls alone spend more than 200 million collective hours per year on this one task. That's hundreds of millions of hours not spent in school, not developing their community and not spent building businesses. A particular loss, considering that in the developing world women-led businesses tend to outperform those run by men.

Illness and chores related to water keep children home from school, often disrupting educators' ability to form those schools altogether as class attendance may fluctuate unsustainably. Without access to water sanitation suffers, as communities can't spare this scarce resource on waste. As a result, tonight more people around the world will use a cell phone than a toilet.

Agriculture is disrupted. Farmers, unable to effectively water their crops, produce less and rely more on synthetic fertilizers which, in turn, further contaminate already precious supplies. Communities, struggling from not having enough to drink, have their problems compounded by food scarcity.

Water shortages are chronic, crippling, and getting worse.

While many Americans see this as a problem for the developing world, one which can be solved by better plumbing and personal hygiene, the reality is that communities across the United States already suffer from fetid and unclean sources. Flint, Michigan achieved notoriety for the leaded tap water that poisoned a city, but rural communities have dealt with similar problems for generations. Water runs cloudy or reeking of chemicals, or filled with detritus, or, from time to time, on fire.

As population growth increases demand and global warming reduces available resources, this problem will only get worse. Years-long droughts have ravaged east and south Africa. Corn production in Zambia (an essential food source for the country) will fall by half this year and the nation's critical hydroelectric infrastructure has all but sputtered out in the wake of declining river levels. Cape Town has watched its largest reservoir slowly dry up with "Day Zero," the day the city will simply run out of water, approaching in 2019.

The World Bank estimates that a city needs about 1,000 cubic meters of fresh water per person per year to maintain adequate supplies. By 2014, Beijing had 145. In 2015, Sao Paulo had less than three weeks of water left before having to turn off access for the entire city. Only a sudden rainstorm spared the city from running out altogether.

Los Angeles famously dumped nearly 100 million "shade balls" into its Ivanhoe Reservoir to try and protect what it had left; the balls should help reduce evaporation and deter algal growth.

Water supplies are getting more scarce. When they run out, it's the poor who suffer. In the developing world, poor communities have to dedicate endless hours to hauling one bucket at a time from far off supplies. In cities, they typically have to suffer whatever comes out of the tap, while wealthier neighbors can afford to buy increasingly expensive bottled water.

While everyone complains if showers slow down and the lawns used to be greener, no one with money goes thirsty or has to skip school. No one with money gets sick because the buckets they use can contaminate even clean supplies, and no one with money would continue to use poisonous infrastructure.

As life's little luxuries get more expensive, only the poor have to watch them slip away altogether. Someone with money may grumble about how a cup of coffee once would cost 50 cents less. Someone without will remember how much they once enjoyed having their morning coffee in all.

Water has received some coverage in recent years. My colleague Anna Clark has written an elegant and powerful book on the subject of Flint, and Water.org's founder Matt Damon has made it a personal mission. Expect many more such works in the future because, without sweeping changes in consumption and environmentalism, this is just the beginning.