Agricultural production often comes at the expense of water quality. As my colleague, Mindy Selman, noted  in a recent blog post, “Agriculture is the leading source of nutrient pollution in waterways—a situation that’s expected to worsen as the global population increases and the demand for food grows.”
But food security shouldn’t come at the expense of water quality—and in fact, it doesn’t have to. This is a topic I’m discussing at a World Water Week  side event, “Securing Water Quality While Providing Food Security: The Nutrient Question.”  Through the use of effective tools and strategies, we have the power to uphold water quality while still feeding a population  that’s expected to reach 9 billion by 2050.
Nutrient Pollution in Water Systems
A variety of agricultural operations contribute  to nutrient pollution  and “dead zones” in freshwater and coastal ecosystems. Fertilizers are oftentimes applied to crop fields at the wrong time in the growing season or in amounts that exceed crop needs, resulting in nutrient runoff to water bodies. Factory farms raising livestock frequently poorly manage or improperly dispose of their manure, allowing it to leach into nearby waterways. And aquaculture operations discharge large amounts of nitrogen and phosphorus from uneaten food, excrements, and other organic waste into lakes and coastal areas.
All of these actions pollute waterways with too many nutrients like nitrogen and phosphorous. These nutrients spur toxic algae blooms that can destroy habitat, cause fish kills, alter aquatic ecosystems, and contribute to “dead zones.” Globally, nutrient pollution of coastal systems has risen  from fewer than 75 systems in 1960 to more than 800 systems today.
Controlling Pollution through Water Quality Management
Efforts to control agricultural pollution must be part of a larger, holistic water quality management strategy  that provides the scientific basis for effective actions, regulatory requirements, and voluntary components where regulatory requirements are not possible or wise. Adequate data on the amounts and types of pollutants reaching surface waters and their impacts on water quality must be collected, followed by the application of reliable, predictive pollutant-loading and water-quality models. These models can be used to support the development of realistic water quality goals, develop and assess alternatives, and inform the selection of strategies to reduce pollutants. The water quality management strategy facilitates the adoption of environmental standards—such as water quality standards and watershed pollutant loading caps—and the implementation of programs to achieve them.
A suite of water quality “tools” directed toward agricultural pollution can play significant roles in this larger strategy. These tools fall into two main categories: technical assistance for farmers and policy instruments.
Tools for Improving Water Quality
1) Technical Assistance Programs for Agriculture
Almost every country in the world has government programs to assist farmers. Technical assistance can include expert guidance on practices like incorporating conservation methods  to improve water management, protecting water quality, controlling erosion, managing manure, properly and effectively using fertilizers, transitioning to organic farming, and applying new technologies. These programs are crucial to both agricultural productivity and environmental protection. Technical assistance programs must keep pace with intensifying agricultural production in their scope and availability.
2) Policy Instruments
Policy instruments for controlling agricultural pollution can be grouped into five general categories:
Regulatory Requirements: With the exception of large factory farms for livestock, there is little direct government regulation of agriculture around the world. Examples of where it does occur include the European Union, where the amount of manure that can be spread on farmland is restricted. The Nitrate Directive  requires member countries to limit the application of manure in Nitrate Vulnerable Zones (areas near waterways that are vulnerable to eutrophication) to 170 kg/hectare/year.
Agricultural Taxes and Fees: These are not widely used, but the most frequent use is charges on agricultural inputs . Belgium, Denmark, Finland, Norway, and Sweden tax pesticides. Europe imposed fertilizer taxes in the 1990s, but has since abandoned them.
Environmental Cross-Compliance: This policy requires farmers to meet certain environmental standards or performance levels if they want to enroll in agricultural support programs like crop subsidies. Environmental cross-compliance requirements are common in the E.U., but have not been very successful in the United States.
Water Quality Trading Programs: These programs are under development  in America and a few other countries. They are a market-based approach where pollution sources facing regulatory requirements to reduce pollutant discharges (such as wastewater treatment plants) can buy pollution reduction credits from other regulated or unregulated sources, such as farms. In this example, the agricultural pollution reductions are frequently less costly to achieve, allowing the wastewater treatment plant to meet its regulatory requirements at lower cost than it would face through facility upgrades. Trading programs can create financial incentives for farmers to reduce their nutrient pollution, thereby helping to improve the water quality of lakes, rivers, and streams.
Green Payments to Farmers: There are two main types of green payments. The first is subsidies for conservation. Many governments around the world provide funding to farmers to engage in conservation practices, like converting  marginal or erodible lands to forests or grasslands, planting grass or forest buffers along streams to trap pollutants, protecting habitats, planting cover crops , or building fences to keep livestock out of streams. The second type is payments for ecosystem services (PES). PES is a relatively new concept that involves paying agricultural or other landowners to preserve or restore  ecosystems on their lands.
Safeguarding Water for the Future
Humans need water as much as food. So the need to feed a growing global population cannot be allowed to impair our ever-scarcer water resources.
Nor does it have to. We can use a suite of management techniques, policies, and regulations to reduce agriculture’s impact on water—and new tools continue to be developed. We just need the resources and will to implement them.