Integrated urban water management

Comparing the natural and urban water cycle and streetscapes in conventional and Blue-Green Cities

Integrated urban water management (IUWM) is a philosophy of varying definitions and interpretations. According to the authors of the book entitled, "Integrated Urban Water Management: Humid Tropics", IUWM is described as the practice of managing freshwater, wastewater, and storm water as components of a basin-wide management plan. It builds on existing water supply and sanitation considerations within an urban settlement by incorporating urban water management within the scope of the entire river basin.^[1] One of the early champions of IUWM, SWITCH is a research program funded by the European Union and seeks to shift urban water management away from ad hoc solutions to a more integrated approach. IUWM within an urban water system can also be conducted by performance assessment of any new intervention strategies by developing a holistic approach which encompasses various system elements and criteria including sustainability type ones in which integration of water system components including water supply, waste water and storm water subsystems would be advantageous.^[2] Simulation of metabolism type flows in urban water system can also be useful for analysing processes in urban water cycle of IUWM.^[2][3]

IUWM is commonly seen as a strategy for achieving the goals of Water Sensitive Urban Design. IUWM seeks to change the impact of urban development on the natural water cycle, based on the premise that by managing the urban water cycle as a whole; a more efficient use of resources can be achieved providing not only economic benefits but also improved social and environmental outcomes. One approach is to establish an inner, urban, water cycle loop through the implementation of reuse strategies. Developing this urban water cycle loop requires an understanding both of the natural, pre-development, water balance and the post-development water balance. Accounting for flows in the pre- and post-development systems is an important step toward limiting urban impacts on the natural water cycle.^[4]

Components

Activities under the IUWM include the following:^[5]

• Improve water supply and consumption efficiency
• Upgrade drinking water quality and wastewater treatment
• Increase economic efficiency of services to sustain operations and investments for water, wastewater, and stormwater management
• Utilize alternative water sources, including rainwater, and reclaimed and treated water
• Engage communities to reflect their needs and knowledge for water management
• Establish and implement policies and strategies to facilitate the above activities
• Support capacity development of personnel and institutions that are engaged in IUWM

According to Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO), IUWM requires the management of the urban water cycle in coordination with the hydrological water cycle which are significantly altered by urban landscapes and its correlation to increasing demand. Under natural conditions the water inputs at any point in the system are precipitation and overland flows; while the outputs are via surface flows, evapo-transpiration and groundwater recharge. The large volumes of piped water introduced with the change to an urban setting and the introduction of vast impervious areas strongly impact the water balance, increasing in-flows and dramatically altering the out-flow components.^[4]

Approaches

• The Agenda 21 (UN Department for Sustainable Development, 1992) has worked out the Dublin Principles for Integrated water resources management in more detail for urban areas. One of the objectives of Agenda 21 is to develop environmentally sound management of water resources for urban use.^[6]
• The Bellagio Statement formulated by the Environmental Sanitation Working Group of the Water Supply and Sanitation Collaborative Council in 2000 include principals such as: Human dignity, quality of life, environmental security, an open stakeholder process, and many others.^[6]
• The UNEP 3 Step Strategic Approach developed in 2005 is based on the application of the "Cleaner Production approach" that has been successful in the industrial sector. The three steps are: Prevention, Treatment for reuse, and Planned discharge with stimulation of self-purification capacity.^[6]
• UNESCO's Institute for Water Education seeks to build on the progress made by the Bellagio Statement and UNEP's 3-step approach by developing the SWITCH approach to IUWM. Components include: the addition of a sustainability assessment, new methods of planning urban water systems, and modifications to planning and strategy development.^[6]

Examples

An example of IUWM is the Catskill/ Delaware water system that provides 1.4 billion US gallons (5,300,000 m³) of water per day, including to all of New York City. The IUWM process included an extensive stakeholder engagement process, whereby the needs of all parties were included into the final management plan. A partnership was created between New York City, the agricultural community, and the federal government. The case has become a model for successful IUWM.^[7]

Grey water systems

Grey water (also written; greywater, gray water, or graywater) is water used with appliances that do not involve or encounter human waste. It gets its name relative to black water which is heavily contaminated with human waste. Different resources suggest what equipment produce grey or black water. However, it is most commonly accepted that bathtubs, showers, washbasins, washing machines, and laundry tubs produce grey water, whereas toilets, sinks, and dishwashers are classified as black water sources.

In 1989 Santa Barbara became the first district in the United States to legalize the recycling and reuse of grey water. Since then, grey water has become a part of integrated urban water management. It addresses the practice of managing wastewater at the residential scale. The premise of grey water reuse is the concept that the average household uses most of its water indoors (roughly 60%), meaning much of that water can be reused to provide for the water required to support irrigation. Additionally, most domestic appliances automatically collect grey water in order for it to be disposed.

There are three types of grey water systems each of which has different requirements, codes, and sizing specifications. However, they share standards to meet health and safety regulations:

The Arizona R18-9-711. Type 1 Reclaimed water General Permit for Gray Water,^[8] stands as the model for grey water system regulation

1. Human contact with gray water and soil irrigated by gray water is avoided;
2. Gray water originating from the residence is used and contained within the property boundary for household gardening, composting, lawn watering, or landscape irrigation;
3. Surface application of gray water is not used for irrigation of food plants, except for citrus and nut trees;
4. The gray water does not contain hazardous chemicals derived from activities such as cleaning car parts, washing greasy or oily rags, or disposing of waste solutions from home photo labs or similar hobbyist or home occupational activities;
5. The application of gray water is managed to minimize standing water on the surface;
6. The gray water system is constructed so that if blockage, plugging, or backup of the system occurs, gray water can be directed into the sewage collection system or onsite wastewater treatment and disposal system, as applicable. The gray water system may include a means of filtration to reduce plugging and extend system lifetime;
7. Any gray water storage tank is covered to restrict access and to eliminate habitat for mosquitoes or other vectors;
8. The gray water system is sited outside of a floodway;
9. The gray water system is operated to maintain a minimum vertical separation distance of at least five feet from the point of gray water application to the top of the seasonally high groundwater table;
10. For residences using an onsite wastewater treatment facility for black water treatment and disposal, the use of a gray water system does not change the design, capacity, or reserve area requirements for the onsite wastewater treatment facility at the residence, and ensures that the facility can handle the combined black water and gray water flow if the gray water system fails or is not fully used;
11. Any pressure piping used in a gray water system that may be susceptible to cross connection with a potable water system clearly indicates that the piping does not carry potable water;
12. Gray water applied by surface irrigation does not contain water used to wash diapers or similarly soiled or infectious garments unless the gray water is disinfected before irrigation; and
13. Surface irrigation by gray water is only by flood or drip irrigation.

A complex grey water system provides for a development with a substantial discharge (greater than 250 gallons) per day. It requires a written construction permit submitted to the enforcing agency.

A simple grey water system is sized to serve a one or two family home with a medium level water discharge (maximum 250 gallons) per day. It too, requires a written construction permit submitted to the Enforcing Agency.

A clothes washer grey water system is sized to recycle the grey water of a one or two family home using the reclaimed water of a washing machine (produces 15 gallons per person per day).^[9] It relies on either the pump from the washing machine or gravity to irrigate. This particular system is the most common and least restricted system. In most states, this system does not require construction permits. This system is often characterized as Laundry to Landscape (L2L). The system relies on valves, draining to a mulch basin, or the area of irrigation for certain landscape features (a mulch basin for a tree requires 12.6 ft²). The drip system must be calibrated to avoid uneven distribution of grey water or overloading.^[10]

Challenges

The biggest concern in Integrated Urban Water Management systems, specifically grey water reuse is the introduction of untreated water into a landscape. It is important that grey water systems maximize natural purification through healthy topsoil, avoiding contact between greywater before and after filtration. Untreated grey water has the capacity to meet runoff and ultimately pollute water systems.^[13]

Research suggests that evaporated grey water can leave microorganisms that can be harmful if breathed or consumed.^[14] It is best practice to not use greywater in a sprinkler system, for this reason. Direct application of grey water can leave the aforementioned microorganisms on foliage. Grey water should not be used on fruits or vegetables (unless applied very carefully and specifically to the roots – although most state codes won't allow this).

Excess grey water which may not percolate into the soil could become runoff often leading the untreated water to waterways. Grey water should not be applied to saturated soil, and should be used conservatively.

Many household cleaners contain ingredients which can't be removed by a typical grey water filtration system. This requires an assessment of which substances will alter the quality of the grey water. Additionally, not all household appliances should be used for grey water recycling. Some should be diverted separately to sewage.

Grey water filtration systems are not equipped to handle the highest levels contaminants. Discretion is required as to when to use the grey water system. This includes consideration of what appliances to connect, as well as how much water is being processed at any given time.

One of the most significant challenges for IUWM could be securing a consensus on the definition of IUWM and the implementation of stated objectives at operational stages of projects. In the developing world there is still a significant fraction of the population that has no access to proper water supply and sanitation. At the same time, population growth, urbanization and industrialization continue to cause pollution and depletion of water sources. In the developed world, pollution of water sources is threatening the sustainability of urban water systems. Climate change is likely to affect all urban centers, either with increasingly heavy storms or with prolonged droughts, or perhaps both. To address the challenges facing IUWM it is crucial to develop good approaches, so that policy development and planning are directed towards addressing these global change pressures, and to achieving truly sustainable urban water systems.^[6]

See also

• Integrated urban water management in Tegucigalpa
• International trade and water
• Water management in Greater Mexico City
• Water management in the Metropolitan Region of São Paulo

References