Deforestation and water quality inextricably linked

Recognition that there is a close link between forests, deforestation and water quality (and quantity) is fuelling calls for more integrated water policies.

The need to halt deforestation is most often heard in the context of increased carbon emissions contributing to global warming. But as scientific knowledge about the role of forests in managing water increases, consensus is emerging that tackling the problem is key to securing quality water supplies too.

Forests make a significant contribution to maintaining high drinking water quality in watersheds by preventing soil erosion. Cutting down trees increases the flow of surface water and transports sediment to streams, silting them up and affecting water quality downstream.

Forests are more effective than other types of land cover in preventing erosion as roots, undergrowth and forest litter trap sediment. Especially on slopes, trees play a key role in preventing landslides and downward soil movements, cushioning the impact of raindrops with their lower canopy leaves.

Forests can protect watersheds from pollution, caused by chemicals from agriculture and industry, or heavy concentrations and organic matter, which cause eutrophication. The UN’s Food and Agriculture Organisation (FAO) maintains that forests are the safest land-use type in drinking-water catchments, as forestry does not normally involve the use of pesticides or fertilisers.

Pollution from diffuse sources, such as industrial and agricultural activities or sewage – so-called ‘non-point source pollution’ - can be reduced by maintaining forests in riparian zones along watercourses.

While the benefits of forests in providing good water quality are generally accepted, controversy reigns over how much they affect water quantity.

The argument traditionally put forward is that conserving forest cover or afforesting upstream watersheds would improve water availability in lowland areas, where demand from households, industry and agriculture is greatest. Forests function like a sponge, regulating the water cycle by absorbing rainfall and releasing it regularly, avoiding droughts and floods.

However, more recent research challenges this assumption, arguing that tree cover can reduce water flow, especially in arid areas. Forests themselves are major consumers of water: the FAO estimates that up to 35% of rainfall is intercepted and evaporated by tropical forest canopies without contributing to soil water reserves.

Towards integrated water resource management

As population growth increases water stress and raises concerns about depleting freshwater resources, policymakers have begun to consider integrated water management plans to incorporate forests.

The European Union’s Water Framework Directive requires member states to develop river basin management plans through cooperation between all relevant national authorities. It also obliges them to pursue water pricing policies that encourage sparing water use while recovering the cost of water services, including environmental costs.

Payments for environmental services are used in many countries to protect forests. For instance, downstream water users can directly compensate those upstream for protecting their water quality.

Home to many endangered species and providers of natural resources and water services, forests gain in value when their worth is calculated in terms of the ecosystem services they provide.

Around 1.6 billion people worldwide depend on forests for their livelihoods, while 60 million indigenous people rely on them for their existence, according to conservation group WWF .

To read more about government water policies, please follow these links:

Water policy

Ensuring drinking water quality standards: From source to the tap

Bottled water quality: bottled water vs tap water

Can desalination technology solve the coming water crisis?

Water quality and availability are inextricably linked

Water quality studies: monitoring our freshwater sources

Harnessing water's potential: What is hydropower?

Water and climate change

Understanding EU Water Directives

Water Filter Reviews