Short answers, pulled from the story.
Groundwater makes up about 30 percent of all readily available fresh water in the world. This amount represents roughly 0.76 percent of the entire world's water including oceans and permanent ice. About 99 percent of the world's liquid fresh water is groundwater.
Water extracted from the Great Artesian Basin in Australia can be more than 1 million years old. This ancient water infiltrated into the ground millennia ago and has been trapped beneath the surface since before human civilization began. The oldest groundwater occurs in the western parts of the basin.
Cities such as Bangkok, Mexico City, Venice, and New Orleans experience subsidence due to groundwater removal. The San Joaquin Valley in California experienced subsidence of up to 9 meters in the first half of the 20th century. Mexico City has experienced rates of subsidence of up to 30 centimeters per year.
Saltwater intrusion occurs when too much groundwater is pumped near the coast allowing denser seawater to penetrate freshwater aquifers. This contamination renders potable freshwater supplies unusable once salt amounts to more than 2 to 3 percent of the reservoir. Many coastal aquifers including the Biscayne Aquifer near Miami face problems with saltwater intrusion.
Groundwater flowing through the Great Artesian Basin travels at an average rate of about 1 meter per year. This slow movement means water can take 1 million years to travel almost 1000 kilometers from the source of recharge. The slow flow highlights the long-term nature of groundwater systems and risks associated with over-extraction.