We're nearly 20 years into celebrating World Water Day, and the issues have only grown more complex -- and in many locales, more serious.

The theme of the United Nation’s World Water Day this year is water and food security. Irrigation for agriculture accounts for 70 percent of the water withdrawn from aquifers, rivers, lakes and wetlands. It takes 1,500 liters of water to produce 1 kilogram of wheat, but it takes more than 10 times that amount to produce 1 kilogram of beef.

The need for investment in water-related technologies, and especially in agriculture, is great. The irrigation rates in many parts of the U.S., Mexico, India, China and Spain are already unsustainable, according to a 2008 World Resources Institute report.  

Although water scarcity is already critical in many regions, the solutions are also readily available. The WRI report found that 85 percent of global irrigation is still done by flooding field or furrows. Sprinkler and drip irrigation can increase efficiency by 70 percent to 80 percent.

China and India combined will soon spend more than $450 billion in water infrastructure, which includes irrigation, as laid out in both countries’ current five-year plans. That’s nearly a 10-fold growth from a decade ago, when the combined spend for the two countries was just $50 billion.

“The emerging market is taking off right now,” said Steven Falci, head of strategy development for sustainable investment at Kleinwort Benson Investors, an Irish investment firm that has been in the water market for more than a decade. He said that the firm is seeing the infrastructure area as the strongest market for near-term growth in water, but certainly not the only one.

Besides installing the latest irrigation technology, making critical upgrades to outdated municipal infrastructure is a driver across the globe. While electric smart grids get a lot of attention, the water grids are often far older and in worse shape. Leakage is greater than 50 percent in some areas. Kleinwort Benson sees this as another ripe area for investment, as companies come up with novel solutions to help municipalities get the most out of their assets. For example, the firm has invested in Pure Technologies, which offers a SmartBall acoustic sensor to find leaks in water systems.

Cutting-edge technology will be essential, as cash-strapped municipalities have to choose between water upgrades and other services. The total cost of infrastructure upgrades for drinking water in just the U.S. between now and 2035 is estimated at $1 trillion, according to the American Water Works Association, meaning water companies will have to work smarter.

The need for smart infrastructure is already resonating in the metering world.

Companies like eMeter and Infosys offer water-specific IT to help manage data coming off of water meters. For eMeter, the water offering will be key as it pushes into international markets after Siemens acquired the company late last year.

One study from Frost & Sullivan estimates the European smart water meter market will be worth $20 billion by 2020 and will see double-digit growth in the next decade. Like electrical meters, new smart water meters allow for end-point feedback that can inform what’s going on throughout the distribution circuit, and can help to monitor usage to comply with local ordinances. Software can also play a role in the water sector -- WaterSmart Software looks to be the Opower of water.

Outside of infrastructure improvements, there are many other areas where investment is expected to grow in coming years. Kleinwort Benson Investors are also excited about ballast water treatment given new standards that may be adopted by the International Maritime Organization.

The new standards would mean the market could grow from $200 million today to $5 billion per year in 2017, according to Danaher, a company that provides UV treatment for ballast water. The new Coast Guard standards essentially call for onboard treatment of ballast water so that foreign organisms aren’t introduced into local bodies of water.

Monitoring water sources for contamination is another area that is ripe for investment, especially with the expansion of fracking, which uses seven times the amount of water as conventional natural gas drilling, but only slightly more than conventional oil drilling, according to the World Policy Institute. The report found that overall evidence is lacking regarding the risk of water contamination from fracking. If many states, such as New York, allow for fracking, the practice could come with regulations that will open the market for water treatment equipment, storage solutions and disposal options.

Wastewater is the last area that should see substantial investment, especially as treated wastewater can be used for irrigation. From 2005 to 2015, there will be a 25 percent increase in the use of treated wastewater or salt water in agriculture and aquaculture, according to the UN.  Wastewater treatment, however, is also energy-intensive, which means that new technologies that reduce energy in treatment plants will be critical in coming years. Emefcy, for example, is a company that has a microbial fuel cell to treat industrial wastewater and was just named a Bloomberg New Energy Pioneer earlier this week.

The power source of energy-intensive activities will also become critical in a water-constrained world. Wind and solar photovoltaic consume essentially no water to produce electricity, while gas, coal and nuclear power plants consume more than 20 percent of non-agricultural water, according to the World Policy Institute. Water management is increasingly on the mind of energy utilities.

As the nexus of food, water and energy becomes more of a focal point for legislators worldwide, opportunities will abound to conserve and invest in new technologies. While this World Water Day is about food security, it is also about cleaner, less water-intensive energy sources to fuel farms, wastewater facilities, homes and businesses.

“Even though we see a nice acceleration,” said Falci, “we think it’s just the beginning.”