Zoom in, and more pockets of concern emerge. States like New Mexico in the U.S. and cities such as Cape Town, South Africa — which nearly ran out of drinking water last year — have "extremely high" stress levels.

Where things stand: A dangerous combination of hot and dry weather, poor water management and rising demand is leaving cities including Chennai, India, and Harare, Zimbabwe, without water for days on end, Tanvi Nagpal of Johns Hopkins writes for Axios Expert Voices:

• "India's government warned in 2018 that 21 Indian cities would run out of groundwater by 2020, placing almost 100 million citizens at risk unless urgent steps were taken to protect and replenish aquifers."
• "Despite the threat of an impending drought, Zimbabwe's protracted political crisis and economic contraction have thwarted major investments in public goods."

What to watch: The pressures on municipal water supplies are likely to worsen with the effects of climate change.

Where it stands:

• Overuse and drought have dried up the 4 reservoirs serving the 9 million residents of Chennai, India's 6th largest city, and the annual monsoon barely eased the shortage. Since mid-July, a daily train has delivered 2.5 million liters of water from a dam 125 miles away, yet many taps have still gone dry.
• The 2 million people of Harare, Zimbabwe’s capital, turn to shallow wells and ditches to supplement the water piped in once a week. Of the city's 4 reservoirs, 2 are dry and the other 2 are so polluted by raw sewage and industrial waste that their water must be heavily treated before piping. A shortage of chemicals has led to a decommissioning of 1 water-treatment plant and inadequate supply from another, as well as an uptick in waterborne diseases.

Between the lines: Weather alone is not to blame.

• Chennai's natural rainwater collection systems and aquifers have been completely neglected. Deep-well drilling by industry and agriculture has gone unregulated, and the government's recent attempts to encourage rainwater harvesting have met with limited success.
• In Harare, decades of underfunding have led to crumbling infrastructure, leaky pipes and widespread water theft.

What's next:

• India's government warned in 2018 that 21 Indian cities would run out of groundwater by 2020, placing almost 100 million citizens at risk unless urgent steps were taken to protect and replenish aquifers.
• Despite the threat of an impending drought, Zimbabwe's protracted political crisis and economic contraction have thwarted major investments in public goods. A good monsoon, together with greater water savings, could avert day zero in the near term, but they are no substitute for long-term planning and investment in water resources and demand management.

The bottom line: Without significant investments in plugging leaky pipes, improving agricultural efficiency, harvesting rainwater and mandating conservation, 45 cities — home to 450 million people — could see their taps dry up by 2030.

Tanvi Nagpal is the director of the International Development Program at Johns Hopkins School of Advanced International Studies.