This piece was co-written with Dr. Larry Brilliant, president of the Skoll Global Threats Fund.

This piece also appeared in McClatchy News and the Huffington Post.

We know less about one of world's most pressing challenges today than we did 10 years ago. It's no secret that water - or the lack thereof - will be one of the defining issues of the 21st century. And yet, the United Nations World Water Report, in 2009, stated that when it comes to water, "less is known with each passing decade."

The World Economic Forum recently named the water supply crises as one of the top risks facing the planet - edging out issues like terrorism and systemic financial failure. Water risks permeate almost every aspect of global society. We got a taste last year with crops scorched by drought, shipping lanes threatened and energy plants shut down by low water levels, and coastlines devastated by flooding. Exacerbated by climate change and population growth, such crises will become more common and costly. Yet, the world largely lacks the data we need to monitor, understand, and respond to these water challenges. We are flying blind when it comes to global water issues.

History shows us the power of information to avert crisis. For example, as a result of a dramatic increase in data, the public health community has transformed its ability to identify and respond to a pandemic. Less than 20 years ago, it took, on average, 167 days to detect and verify a disease outbreak.

Today, it takes less than 20 days largely because of advances in data collection and availability, including leveraging passive data through tools like Google Flu Trends and web scrubbers like the Global Public Health Intelligence Network. The health sector has invested in better information to detect pandemics. It's time for the water sector to invest in better water data to respond to devastating water-related disasters and increasing water risks.

Unfortunately, directly observed data on water is patchy at best, non-existent at worst. The Global Runoff Data Centre is the closest thing to an international clearinghouse for information on how much water is in rivers worldwide. But the number of data collection stations reporting to the Centre has fallen steadily since the 1980s; only about one-third of the observing stations report their data to the Centre. Many stations are no longer being maintained, have been eliminated, or are reluctant to publicly share the data. Of particular concern are the region's most at risk - the Middle East, South Asia, and Africa - where publicly available water data is nearly absent.

Even in the United States, the story is not so different. The country is still recovering from impacts of Superstorm Sandy, which cost over $60 billion, and the ongoing drought, which may turn out to the be the costliest natural disaster in U.S. history.

Meanwhile, the U.S. Geological Survey reported that between 1980 and 2004, over 2,000 stream gauges to measure river levels were shut down, a loss of more than a quarter of the nation's total network. These gauges help predict floods and droughts and provide the data needed to monitor changes in water stress. The current budget "sequestration" could force USGS to shut down an additional 375 gauges.

To prepare for an increasingly water-insecure future, we urgently need to bridge this data gap.

The good news is we do not have to start from scratch. Using available data from satellites and state-of-the-art modeling techniques, it is possible to collect critical information needed to monitor and evaluate emerging water risks across the globe.

One example is Aqueduct, the global water risk mapping tool recently released by the World Resources Institute, with the support of the Skoll Global Threats Fund, and multinationals like Goldman Sachs, GE and Shell. Aqueduct offers free and open data, across twelve indicators of water risk, ranging from floods and droughts to access to clean drinking water. It also provides the ability to project changes in water risks in the coming years, according to the effects of climate change, and population and economic growth.

While Aqueduct represents an important resource, it is not enough. There is no substitute for directly observed, locally collected data. Bringing together such information can be a daunting task, but there are several important steps that must be taken to improve water data. We need increased investment in gathering local water data; and more stream gauges need to be installed, rather than shuttering those we already have. We need to meter groundwater, so we know how quickly these water suppliers are being depleted. We need to take advantage of new technologies, such as satellite remote sensing and crowd-sourced data, to fill the gaps. And perhaps most important, we need to change the paradigm from secrecy to transparency by negotiating ways to make existing data held by governments, companies and academic institutions freely available.

In 2012, a UNESCO report compared our understanding of water to "islands of knowledge in a vast sea of unknowns." As we mark World Water Day 2013, it's clear that this is no way to handle one of the defining challenges of our generation. Now more than ever, we have the capability to address our woeful lack of water data. We just need the will to do so.