Introduction
Water is a vital resource used around the world for domestic, industrial, agricultural and leisure and amenity purposes. However, only an estimated <0.32% of 1.4 million km3 of the world’s water residing in shallow groundwater (0.3%), lakes (0.01%) and rivers (0.0001%) is available for human use. Of these potential sources, most is either difficult to access or is distant from areas of demand. In recognition of the importance of water resources, most industrialised countries adopt national strategies to control water use and to ensure that the quality of the water is fit for the use intended.
Abstraction controls, environmental and legislative drivers to reduce water use or to recover and re-use water, and appropriate pricing are measures governments can impose to control supply stresses. Limiting water contamination both from identified sources and the control of diffuse non-specific pollution ensures water quality can remain satisfactory even if re-used extensively.
In this article we focus on the pressures on UK water abstraction from surface sources and ground water. Strategies to manage these pressures are reviewed with specific reference to land management techniques. The stresses on water resources are identified in terms of water quality and water demand. The major regulatory strategies to control and minimise these water stresses in the UK are identified.
Water demand and supply in England and Wales
The UK Government recently published its water strategy for England (“Future Water”, DEFRA, February 2008). This evaluates water stresses in an area of the country with limited water supply and a high demand, which are particularly severe in the South East and the East of England. The strategy, covering a period up to 2030, discusses the demand and quality issues of interest in this review. Future Water also incorporates climate change into its considerations, and addresses flood risk management and control.
Current levels of water demand in England and Wales are about 1 tonne/person/week (Waterwise, 2006). This is one of the higher usages within the EU, being similar to France (150 litres/person/day, l/p/d), but greater than Germany (127 l/p/d) and much of Eastern Europe. Public supply demand in England & Wales comes largely from household use (see Figure 1), although significant amounts are wasted in leakage.
Approximately 18 billion tonnes of water are taken annually from reservoirs, rivers and aquifers in England. One third goes to public water supplies, and half for electricity generation, although much of this use is non-consumptive and abstracted water is released back to the environment after appropriate treatment. In contrast to domestic demand which has increased steadily since the 1950’s, as population has increased and consumer behaviour has changed, industrial and commercial water use has declined during the same period, currently standing at 2.1 billion tonnes annually. Agricultural demand, approximately 0.2 billion tonnes annually, has resulted in near constant abstraction for about 30 years. Although overall the demand from agriculture is relatively small, regional variations mean that some parts of Eastern England, for example, can have significant local impacts.
Over the next two decades, demands for water are likely to increase. The UK is implementing policies to increase its housing stock to meet population growth and other social needs. At the same time, predicted rainfall in some of the highest water demanding regions of England may fall by up to 50% in the summer months by 2080, although the model predictions come with significant uncertainties.
Clearly, one important focus for the national water strategy is to reduce waste from suppliers and domestic consumers. Water management to reduce demand, to use high quality water more sensibly, and to alleviate flood risk, is an important aspect of new housing and commercial development. The national strategy aims to reduce nationwide demand to 120-130 l/p/d through improved management and technological developments by 2030. Water suppliers are adopting their own water resources management plans (WRMP) to deliver sustainable supplies over a 25-year time-scale.
Pressures on abstracted water quality
Water quality has improved in the UK in recent years as more effective monitoring has identified threats and regulation has reduced discharges to the environment. Particular success has been met with the control of point-source discharges from the water and other industries. Implementation of Integrated Pollution Prevention and Control (IPPC) means that releases of a wide range of controlled substances, including toxins, metals and persistent organic pollutants are prevented, whilst inputs of suspended solids and oxygen demanding wastes are restricted so that impacts on the receiving environment are reduced to an acceptable level.
Licensing of industrial discharges to sewer has helped to protect sewage treatment works from shock or toxic loadings, improving their reliability. More recent concern has focussed on the continued discharge of identified endocrine disrupting chemicals (EDC) from wastewater treatment works, many of which are incompletely removed by treatment processes. Yet more potential EDC remain to be identified.
Groundwater protection has also advanced in recent years. The Groundwater Directive is considered within IPPC licensing, as the threats to groundwater from large scale industry from chemical spillage are specifically addressed as part of permit drafting. Local Authorities are required to identify contaminated land areas under the New Regime, where pollutant migration routes to groundwater form part of their assessment.
Water quality impacts from diffuse sources are more difficult to regulate and manage. Nutrients, primarily nitrate and phosphate, are flushed from agricultural areas in a complex manner, with nitrogen in particular undergoing several chemical transformations within the soil prior to leaching. Agricultural pesticides can also enter surface waters through drift and leaching unless carefully managed. Urban diffuse pollution can introduce a range of oils, organic particles, EDC and other harmful substances to exposed surface and ground water.
Diffuse pollution is subject to a variety of natural influences including soil structure and rainfall amount and intensity. High rainfall can increase pollutant leaching to a receiving water environment. Low rainfall or excessive abstraction from surface water, however, can decrease pollutant dilution and exacerbate its impact. Land management techniques together with the adoption of environmentally sensitive practices offer the best solutions to controlling diffuse pollution.
Land management techniques for controlling water pollution
Abstraction licensing, originally adopted in the 1960’s, has been recently updated through the phased implementation of the Water Act 2003 and is a key method of managing water demand. Since October 2001, licences granted have been issued with a time-limit, the expiry of which would normally mean re-issue of the licence. Further review of abstraction licensing will occur in the future as River Basin Management Plans (RBMPs) are adopted.
RBMPs determine how water resources are to be managed in an integrated way over the coming decades. The main platform for the implementation of this is the Water Framework Directive (WFD). In addition to diffuse and point-source pollution, pressures on water resources from physical changes, excessive abstraction, and non-native species invasion are the focus of WFD. The WFD aims to look holistically as the impacts of water resource use on water ecosystems. Through the Environment Agency, RBMPs are being developed in consultation with a range of stakeholders. This has resulted in the establishment of environmental quality standards and agreed methodologies for assessing the economic and environmental costs and benefits of activities within specific river catchments. RBMPs are to be generated for each river basin on a 6-yearly cycle. Draft RBMPs are currently issued for a 6-month consultation, with approved final RBMPs due to be published in late autumn 2009.
The outcomes of WFD implementation are wide-ranging. Improved point-source sewage nutrient treatment in areas particularly sensitive to eutrophication have been identified, and there is a commitment to reduce the input of phosphorus to sewage through improvements to cleaning-product formulation. Greater use of reed-beds and wetland preservation will reduce the impacts of suspended solids and COD releases, whilst these also form the basis for important microbial reactor zones for denitrification and for the absorption of persistent contaminants. Inputs to the sewer system under Mogden formula charging schemes will be reviewed to ensure they meet WFD requirements.
Diffuse pollution management under the WFD will rely heavily on land management techniques and operational practice measures. Agricultural diffuse pollution has already been addressed in certain areas with the introduction of Nitrate Vulnerable Zones (NVZ). These areas were identified as having, or being susceptible to, surface water or groundwater nitrate concentrations in excess of 50 mg/l, the limit set under the Nitrates Directive (1991). In NVZ, improved farming practices for fertiliser and manure reductions and application timings and methods were the key mechanisms to successfully reduce nitrate pollution threats. Extension of the NVZ into the wider WFD regulatory framework is currently under review. However, some of the practices first supported within NVZ have evolved into the more widely scoped Catchment Sensitive Farming (CSF). Following a two-year voluntary scheme supporting farmers adopting CSF under Environmental Stewardship schemes, a further three years of DEFRA initiatives and support is proposed.
Under CSF, the responsible use of fertilisers, manure and pesticides is retained. Other land management techniques are also promoted. Improving soil structure and reducing erosion through contour tilling, and the planting of cover crops are example measures. The assignment of riparian buffer strips provides an important interception and reactor zone for leached contaminants and solids, although issues with potential through-flow remain and it is not always practicable to introduce buffer strips of sufficient width to completely contain contamination. Other procedural initiatives, for example, reduction of livestock density thus reducing soil compaction and overgrazing, act to improve diffuse pollution control. CSF also promotes improved yard and water management on farms through the separation and appropriate routing of clean and dirty water.
Water abstraction is now licensed by the Environment Agency in line with the appropriate Catchment Abstraction Management Strategy (CAMS). Each regional CAMS outlines the likely approach the Agency will take to abstraction licence renewal upon expiry. Each regional CAMS is a systematic review of current water abstraction licences issued (i.e. all abstractions >20m3/day), together with a considered assessment of the impact of abstraction on habitats and biodiversity for each river system within that region. In each case, water is defined as being either available for abstraction or not, and where it is an evaluation of whether abstraction is currently acceptable, over-licensed or excessive is made. Zones of detrimental abstraction impacts are identified, and CAMS indicates the likely outcome of licence renewal applications based upon the objectively assessed geographical location. Since existing abstraction licences are time-limited, review under CAMS will roll-through and this aspect of catchment management will iteratively reduce diffuse pollution in under-pressure areas derived from over-abstraction.
Urban diffuse pollution will be addressed in part through the adoption of Sustainable Drainage Systems (SUDS). The key objectives of SUDS are to reduce flood-risk pressures by controlling run-off from roads, pavements and roofs, to prevent contaminant transport to surface waters, and to ensure river base-flow is not unduly decreased through the excessive diversion of rainfall through piped systems. SUDS aim to moderate run-off and filter contaminants, simulating natural water detention and infiltration largely through engineered land management solutions.
Permeable pavements permit a steady infiltration through a porous hard-standing surface layer either to underlying subsoil or a storage or detention reservoir. Filtration removes a degree of contamination, whilst run-off rates are reduced. Similarly swales, grassy ditches used to detain and infiltrate run-off, are well suited to construction in housing and commercial developments in place of kerbing. In larger developments it is possible to connect swales to a wider drainage network comprising ponds and wetlands. These areas offer potential for controlled water detention and also afford amenity benefits for local communities. In the UK, pressures on space and high land costs mean the extensive drainage networks, as constructed in Sweden and elsewhere, are not always feasible. Costs are often more acceptable though, when viewed properly against conventional alternatives, as described below. Storm-water detention from roads is achievable by constructing infiltration trenches. In practice infiltration trenches are often combined with filter strips which intercept much of the inflowing solids to increase trench lifetime and performance. The scope for using SUDS on brownfield redevelopment is, however, restricted should the migration of pollutants from contaminated land be a risk.
Hidden infrastructure
CAMS offers a key methodology for managing water demand. Land management techniques offer solutions to improve water quality currently compromised by rural and urban diffuse pollution. New approaches can be subject to considerable inertia because of perceived or real financial concerns. SUDS implementation is a good example of this and, for example, in the South East of England where large scale housing development needs have been identified and land costs are relatively high, a more thoughtful approach is required.
“Hidden infrastructure” is a concept recently advanced by the Environment Agency. Its aim is to highlight the environmental services required to support new developments, particularly housing, the costs of which can be largely unnoticed. Water supply, wastewater and solid waste disposal and treatment and flood protection are all aspects of the environmental infrastructure required for these new developments. Estimated costs per house for these services in South East England are GBP1700, 13000, 100 and 5400 respectively (Environment Agency data, 2007). Developers and water suppliers must consider these hidden costs and pressures in their planning. DEFRA’s “Making Space for Water” initiative (aimed primarily at flood control) aspects of SUDS including green roofs, grey-water reuse, currently pilots an integrated approach to urban drainage.
Technological advances to improve water re-use
Water audits are reportable by a wide range of industrial sectors under IPPC. Implementing remedial improvement conditions to enhance water use reduction and process water re-use will further improve industrial performance in this respect. Wastewater treatment standards are also closely regulated to control the quality and quantity of discharges to sewer, to groundwater and to surface water.
Advanced new technologies are available to allow these high standards of wastewater treatment to be achieved. For example, improved solids removal and COD reduction is technologically and economically feasible using microfiltration, ultrafiltration and even nanofiltration technology in combination with appropriate membrane bioreactor technologies. Many new technologies are designed so they can be retro-fitted into existing treatment schemes; they typically have a small footprint to fit into restricted space, and generally have low maintenance requirements and are suited for remote operation. The market offers operators a wide range of technical solutions for most system capacities. Specialised treatment for nutrient or metal removal, for example using passive wastewater filtration through sorptive media, or hard COD treatment using catalysed UV photo-oxidisation, mean that even difficult wastes such as landfill leachate can now be reliably treated.
High quality on-site wastewater treatment improves the scope for water reuse in many industrial sectors, simultaneously reducing the pressure on receiving water and sewers from high volumes of discharges. The polluter pays principle can apply in a direct manner.
Conclusions
Current demands on water supply in the UK are set to increase. Abstraction from rivers, reservoirs and groundwater for domestic, power generation, industrial and agricultural purposes impart stresses on local water resources, as does pollution from point and diffuse sources. In the UK, as elsewhere in Europe, the WFD sets out aims to manage our water resources holistically. Implementation of the WFD has begun with reviews of discharge consents being measured against new environmental quality standards aimed at site-specific ecological protection. Advanced treatment technologies allow operators to meet new stringent consents. Groundwater protection, already in place with existing IPPC and other regulation, is likely to be enhanced with a new Groundwater Directive in due course.
Diffuse pollution remains a difficult pressure on water resources to manage effectively. Land management techniques used in the past, including the introduction of NVZ and the support of good farming practice met with success in achieving its goals. The potential extension of NVZs and the adoption of “Catchment Sensitive Farming” build upon prior success in minimising rural diffuse pollution using a range of land management and procedural approaches. Sustainable Drainage Systems will similarly address aspects of urban diffuse pollution whilst simultaneously meeting flood-risk alleviation objectives. Time-limited abstraction licences issued in line with Catchment Abstraction Management Strategies will ameliorate the detrimental impacts on habitat quality for the most demand-stressed river basins. Under the overarching WFD these land management techniques offer an important solution to diffuse pollution control, and will contribute to optimising water extraction in the future.