There is likely no single or simple answer. It’s just one example of the general issue of humanity living beyond its means, filling the deficit by drawing down on resources that will not be renewed. Debt and bankruptcy is a good analogy.

In a way, this is quintessential human behavior. Animals faced with shortages tend to die off until their population size matches the available resources. Humans have invented ways to postpone this fate, manipulating our environment in order to sustain a growing population.

So it’s not “just” infrastructure mismanagement. Unsustainable living is practically ingrained into human nature.

The challenge will be whether we can voluntarily reduce our population size or consumption to match the available resources, or whether we’ll have that reduction forced upon us.

If we could put ourselves in the shoes of the people in charge in these places. We'll probably all agree we as the Government have a vested interest in maintaining social stability. One key to this is maintaining access to potable water. Sick and diseased people won't rebel, but they'll be unable to carry out ordinary functions, you'll be vulnerable to outside forces. In periods of drought access to food is affected, the population might get restless, again, we'll be happier if they're placid so let's make sure water is available. If we know our water system is threatened we'll use any method available to ensure access to water is not interrupted. Seek advice of a soothe-sayer, sacrifice to the gods, take IMF loans, go to war with a neighbor. If none of these things is successful, the situation is dire. The people will become dissatisfied, if they organize and obtain weapons we could see violence. At worst we could lose our heads, or at best flee to a wealthy country but leave behind our power. Therefore, we'll appoint our best people to manage and maintain our water system.

Climate change is also a pretty big deal in a lot of places - if you rely on a snowpack melting for water, and it doesn't snow anymore, c'est la vie

Washington State (and California?) gets its summer water from snowpack, not rainfall. If there's no snowpack, then we'd need massively larger reservoirs to hold water. I think it's more nuanced than "mis-management or under-investment".

Where I live there plenty of water but as it's a bit warmer algal blooms are more common. There's also an increasing amount of fertilizer that end up in the water which.makes it worse.