Water is a very California problem at the second... Not every part of the USA is in drought
Water is a problem in many places. I do grant writing for nonprofit and public agencies and have worked on a bunch of water well projects (and have in fact been working on a water project today). They're much more interesting and technically sophisticated than you might imagine, and water tables have been dropping in much of the country. Wells are also easily fouled. Fracking has been a problem for water wells in many parts of the country.
Right now, wells cost a lot of money to drill—often more than $10K—and are easy to screw up. That may be part of the reason YC is looking for water-related startups.
Besides California, and staying in the US, water is also an issue everywhere in the Southwest (Colorado River basin, a quarter-million square miles), and throughout the agricultural midwest, from Nebraska to Texas, where water is being over-drafted from shallow portions of the continent-scale Ogallala Aquifer (https://en.wikipedia.org/wiki/Ogallala_Aquifer#Aquifer_water...).
Too much water can also be just as devastating as too little water. As our climate warms, more energy will be stored in atmospheric and oceanic waters, creating more powerful hurricanes and storms. On top of that, sea level rise will cause storm surges to be more destructive and costal erosion will gradually sink major costal cities. Climate change is water change.
Water is a problem in many places. I do grant writing for nonprofit and public agencies and have worked on a bunch of water well projects (and have in fact been working on a water project today). They're much more interesting and technically sophisticated than you might imagine, and water tables have been dropping in much of the country. Wells are also easily fouled. Fracking has been a problem for water wells in many parts of the country.
USGS has much of the better and more useful data about water quality: https://water.usgs.gov/nawqa/studies/domestic_wells.
Right now, wells cost a lot of money to drill—often more than $10K—and are easy to screw up. That may be part of the reason YC is looking for water-related startups.