Do you know where your drinking water comes from? If you’re like millions of Californians, then the answer is no.

As KQED Climate Watch’s Craig Miller reported last week, a new statewide poll asking residents about the Sacramento Delta — an immense waterway north and inland of the San Francisco Bay Area — revealed that most people don’t know anything about the Delta and that “only 2.3% cited the Delta as a “source of water.”

It’s shocking, considering that the Delta helps shuttle fresh water to more than 25 million people in the state. It’s also an essential water resource for agriculture in Central and Southern California.

The confluence of three rivers (the San Joaquin, Old and Middle Rivers) in the Sacramento-San Joaquin Delta. This system supplies two-thirds of California’s drinking water as well as 50% of the state’s agriculture. Credit: Brothergrimm/flickr.

But really, who cares if you don’t know where your water comes from? After all, good, clean drinking water has always been as close as your kitchen faucet, so it’s long since been figured out, right?

Not quite. Water supplies are sensitive to a lot of different factors, including extreme weather and an evolving climate. As global temperatures rise, regional changes could have a growing impact on access to clean water.

In California, for example, a projected decline in winter snowpack over this century means there will be less fresh water coming down from the mountains to the Sacramento Delta during the summer, when the water is needed most. Moreover, sea level rise around the San Francisco Bay region could send saltwater further up into the Delta, where it will mix with and taint the fresh water.

In other parts of the U.S., freshwater supplies are also vulnerable to the effects of climate change:

• New Yorkers rely on upstate rivers and streams for their water. Yet, researchers project that heavy downpours will increase over the next several decades (they’ve already been rising the past 50 years) and this intense rainfall could make flash floods more common. Drinking water can be easily polluted if floods overwhelm stormwater systems. And even though episodes of heavy rain are expected to increase, total summer rainfall is likely to decrease, which could spell for summer droughts and water-use restrictions.

• In Florida, underground aquifers (or reservoirs) provide Miami’s water, but rapid sea level along the state’s southeast coast could increasingly push saltwater into the freshwater supplies. In recent years of drought, like 2006-2007, saltwater has intruded into an already limited freshwater supply, revealing just how vulnerable Miami’s water resources are. In the future, periods of intense drought mixed with the rising seas could lead to water shortages across Southeast Florida.

• The Colorado River and its tributaries are an essential water resource for millions of people living in America’s Southwest. Yet, a recent review from the Bureau of Reclamation points out that region is bound to face reduced water supplies in coming decades. Ever-warming temperatures and shrinking snowpack will be particularly troublesome when it comes to storing enough water to meet late spring and summer demands, the report says.

In many areas, the groups that manage water resources are catching on to the risks that climate change pose to our water supplies. Cities like Miami are looking at how it can conserve water to help fend off the inward seep of saltwater. New York is looking to update its stormwater systems to minimize pollution during floods.

But according to Kathleen Miller, an expert on how climate change will impact water from the National Center on Atmospheric Research, not all regions have looked into what rising global temperatures means for local water supplies.

“Among water resource managers, there is quite a wide range of perspectives on this and whether this is a problem that needs to be taken seriously,” Miller said.

Even with some uncertainty on just how severely water resources will be affected by climate change, Miller says water shortage risks should inspire water managers to find a robust plan for the future.

Considering that access to clean water is among our most basic needs, you might think about looking into where your water comes from. Otherwise, if your local water utilities aren’t planning for climate change, you’re bound to be surprised if the water starts running short.