Can you imagine a day when you turn on your faucet and no water comes out? The hypothetical question, posed by a research team at UNLV, is called a Day Zero scenario. It sounds like the plot of a doomsday apocalypse series but its not as unimaginable - or as far-fetched - as a Hollywood screenplay might seem. A few years ago in Cape Town, South Africa they almost reached this point, where they were about to tell their citizens that they simply had no more water to give them, even though we all know that water is necessary on a daily basis, said Erica Marti, an associate professor of civil and environmental engineering.