 Our renewable supply of fresh water comes from precipitation over land. It's fundamentally a process in which solar energy causes water to evaporate from the seas, which then comes to us and provides us with the fresh water no longer saline that we need. The areas in red in the diagram that I'm showing are already using 100% of what they're getting renewably. And you can see that these regions include rich countries and poor countries that developed in the developing world. The pressure on water has tightly coupled the production of food. More than 70% of the world's water withdrawal, fresh water withdrawal, is for growing food. And much of that use is not really very efficient. But the impact of human water withdrawals has already been devastating around the world. We have, for example, the ROC in Central Asia. The rivers feeding were diverted for agricultural purposes. It's dried up. The cities around it, the economies based on it are gone. And this was the fourth largest freshwater lake in the world. And on this, we have a growing population. When I was born around 1960, the world population was about 3 billion people. Today, it's 7 billion. It will be 9 billion by 2050. But that 3 times the number of people require far more than 3 times the amount of food. Because of development and because richer people tend to eat richer diets. Now, we've managed so far through technology. We have, for example, developed fertilizers by using a lot of energy. We used a lot of water to irrigate. And through this, over the past half century or so, we've had a green revolution. We've managed to reduce famine, to reduce malnutrition, and so forth. But the cost has come in energy. For example, about 1% of the world's energy is used to produce fertilizer. And beyond the energy cost, there's been a cost in water. Because the fertilizers run off into water supplies. And the fertilizer that feeds the growth of plants also feeds the growth of algae. Algae produces toxins that can poison water supplies. It depletes oxygen, which can kill fish. In the Gulf of Mexico, the dead zone that results is sometimes as large as 20,000 square kilometers. In addition, energy consumption, energy production consumes a lot of water. About 40% of the freshwater withdrawals in the United States are for the purpose of cooling power plants. And with this, then, we have additional pressure in growing populations to consume even more water. Energy can compete with agriculture, it can compete with cities for water, particularly in dry climates. With urbanization, people find it easier to use water, and perhaps not even to use it carefully. In developed countries, the per capita consumption of water can be 10 times higher than in developing areas. It's projected that by 2050, 70% of the world's population will live in cities. And so cities are particularly challenged in finding more efficient ways to use water. But for all of this, the planet is covered in water. We have a lot of it. The hitch is that most of it is too salty for us to use directly. And so desalination may be a very important part of the solution, especially for coastal cities. And in fact, we know how to desalinate water. It's done in a number of places. For example, in Coquipó, in the Aracama Desert in Chile, the local river has been dry for about 15 years as a result of diversions of water for mining and for agriculture. So they now desalinate, as shown in this photo. At MIT, we have a fairly extensive program looking at ways to make desalination more energy efficient and more affordable. In fact, we have even been looking at the question of whether we can make energy from the differences in salinity between freshwater and seawater, so that where a river meets the sea, you might be able to generate power. Worldwide, the capacity of this type of power generation has been estimated to be twice the capacity of the current electrical generation in the United States. Nanotechnology also has a role in this. The diagram I'm showing illustrates a sheet of carbon atoms, one atom thick. It's called graphene. MIT researchers have discovered that they can use graphene sheets to separate water molecules from dissolved salts, potentially providing much more efficient means of desalination. We've also looked at biomimetic membranes using plant xylem, which may provide low-cost water filters for the developing world. But if we're going to do all this, renewable energy really needs to be part of the sourcing, and driving desalination by solar or wind power is essential to avoiding an increased carbon footprint. Beyond desalinating water, we have to think about wastewater. In the United States, shale gas and shale oil have transformed our energy profile, but the process consumes a lot of water, produces a lot of wastewater, and it's considered to be a major environmental hazard. MIT researchers have actually spun out a company to remediate this water in a zero-liquid discharge process currently operating in Texas. And finally, we have sewage, which is mostly water. And it is possible to separate the water from sewage for less energy than desalination. In fact, this is done in a number of places in the world. It is of great interest to many more places because it is relatively more energy efficient. But people don't seem to like it. So we have a question then. As we look at cities, particularly coastal cities, should we be thinking about doing more with wastewater recycling, or should we focus instead on a more acceptable alternative in solar desalination? Thank you.