Water issues are complex and interrelated, so it can be difficult to solve them. But because water is essential to our way of life, we gotta get to work!
Here's an example of how convoluted things can get:
A study at the University of California in Irvine found that freshwater runoff (from precipitation and ice sheet melting) into the oceans has increased significantly--18% more water flowed into the oceans in 2006 compared to 1994. The main problem with this is that the freshwater then becomes saltwater, and we have to wait for it to evaporate and rain onto the ground for it to become drinkable/cookable/agriculturable again. But with global warming, precipitation patterns have changed so that the areas that need water aren't getting as much as they used to.
Speaking of global warming, CO2 in the atmosphere does more than heat things up--it dissolves into the ocean, which makes the water more acidic. This change in pH, though subtle, could become sufficient to kill delicate creatures such as krill in the Southern Ocean within 100 years. Considering that many of the fish we like to eat dine on krill, this could pose a big problem in the future.
But it gets more complicated. The runoff from agricultural fields contains nitogren-based fertilizers, and rivers release tons of it into the ocean each year. The nitrogen fuels an overgrowth of algae, which die when the nitrogen is gone and fall to the seafloor. There, they are consumed by bacteria that thrive and gobble up all the oxygen, creating a "dead zone" where plants and animals cannot live. While human activities add double the natural amount of nitrogen into soils, about 60% of that fertilizer is never used by the plant and ends up in the ocean. Some of it also ends up in the atmosphere, where it becomes N2O--a more powerful greenhouse gas than CO2. This adds to global warming, bringing us back to increased freshwater runoff.
In short, more water is running into the ocean and that water is full of ick that kills stuff and makes more water run into the ocean. Ick.