BACKGROUND PAPER ON WATER REUSE

The Basic Challenge and the Potential for Water Reuse

Water is a necessity for both individual and community well being. As population grows, water needs increase and fresh water sources become taxed to the limit. As a result, many regions have been forced to reassess the long-term reliability of their water supply systems. In addition, there is a growing recognition of the need to restore and preserve our aquatic ecosystems by allowing larger volumes of water to remain within the banks of the streams plunging down from the mountains and all the way to the sea (Wright et al. 1995). Thus water resource and management issues are becoming increasingly critical. The water resource challenge might be stated as how to

1. maximize the use of fresh water resources for the production of potable water and

2. maximize the use of potable water for applications requiring potable water quality.

According to a 1990 USGS report (USGS 1995) the delivery of water to different use categories was:

Category
% delivered
Domestic
57
Commercial
15
Public Use and Losses
14
Industrial
13
Thermoelectric Power
1

Residential uses of drinking, cooking, bathing, laundry, and dishwashing account for about 40% of the total domestic use (Sanders et al., 1993).  The other 60% is about evenly divided between toilet flushing and outdoor use. Reclaimed water could be used for this 60% segment of domestic category, or about 34% of all water delivered.

A sizable portion of the commercial and public use is also for outdoor use and primarily for irrigation. It has been estimated that as much as 40% of the total water use nationwide is for agricultural irrigation. This is another area for possible water reuse, provided water quality does not lead to crop loss.

The 13% of potable water delivered to industrial users is also an area for possible water reuse. Potable water accounts for about 19% of industrial water use (USGS, 1995).

In total, perhaps as much as 50+% of potable water use can potentially be met by water reuse. This does not mean that all these applications are technically, economically, socially, and political feasible; however, it does indicate the large potential importance of water reuse as a water management tool.

Figure 1 presents two extremes in management of water resources to meet water needs. In situation #1, only fresh water resources are used to meet all water needs, and there is no reuse of water. This situation is rarely encountered, due to some amount of water reuse (such as use of wastewater treatment plant (WWTP) effluent for irrigation) and some use of lower quality water resources (such as in desalination of brackish water or seawater). Situation #1 represents inefficient management of water resources where feasible alternatives exist. Contrasted with this picture is the second situation, where maximum utilization is made of all feasible water source alternatives, including the following:

1. Use of lower quality water sources to produce drinking water

2. Use of lower quality water sources to meet non-potable water needs

a. Where treatment is not required

b. Where treatment is required

3. Reuse of WWTP effluent

a. Where treatment is not required

b. Where treatment is required

4. Use of recycle within non-potable uses

a. Where treatment is not required

b. Where treatment is required

Situation #2 represents the extreme in efficient management of water resources. The present state of water resource management is somewhere between these two extremes, with a growing recognition for the need to move toward more efficient management.

Water Reuse and Other Definitions

Unfortunately in the literature there are different definitions of water reuse and water recycle that can lead to confusion. Thus it is important to settle on definitions when discussing these terms. ‘Water Reuse’ is defined by a Florida statute as the deliberate application of reclaimed water for a beneficial use. For many, the term more narrowly means the use of WWTP effluent. However, in its broader meaning it includes the reclamation and recycling of any water by any entity (municipal, industry, commercial establishment, etc.). We use the term ‘reuse’ in this broader meaning. The term ‘recycle’ may mean re-use of water with minimal if any treatment (such as in the pollution prevention and waste minimization fields). We will use the term, however, in its broader definition, simply meaning the subsequent use of water following its previous use - whether or not it is treated prior to its subsequent use. Standard use of the term ‘reclamation’ implies treating and we use the term in this way. Thus, our usage of the terms is:

Water Reclamation: treatment of water after a use — whether or not the treated water is reused

Water Reuse: treatment of used water (reclamation) and subsequent use of it (any water by any entity)

Water Recycle: subsequent use of previously used water whether treated or not prior to the subsequent use; this is thus a broader term than the term ‘reuse,’ which implies treatment prior to subsequent use

Practice of Water Reuse and Recycle

Water reuse practices vary considerably from location to location depending on regulations in place, available water resources, and population and other indicators of water need. Many countries have reuse programs, and some countries, such as Japan, have highly developed programs (Goto, 1995). California and Florida are the most active reuse states, as indicated by the volume of water reused. They maintain inventories of reuse projects by reuse application.

There are many reuse applications. Table 1 is a list of recycled water (from WWTP) uses allowed in California (WateReuse Association, 1999), with a few added applications from the literature. No distinction is made in Table 1 for the treatment level required for each application. The four treatment levels range from undisinfected secondary to disinfected tertiary. The uses in Table 1 are not separated according to the nature of the user (commercial, residential, industrial, municipality, etc.). These categories of use are discussed next.

Urban Reuse

The more common applications include irrigation of public access areas (residential lawns, parks, school yards, highway medians, golf courses, and landscaped areas surrounding hotels, offices, and commercial buildings). Other uses have included vehicle washing facilities, reflecting pools and fountains, fire protection, and toilet and urinal flushing. Urban reuse systems typically involve dual distribution systems that deliver reclaimed water to customers in a network of distribution piping separate from the potable distribution system. Examples of such systems are the Irvine Ranch Water District in California and the cities of St. Petersburg and Cape Coral in Florida. In St. Petersburg, Florida the dual distribution system has reduced potable water usage by 50%.

Agricultural Reuse

As Table 1 reflects, there are several different agricultural reuse categories. California and Florida have extensive programs accounting for between 34 and 63% of the total volume of reclaimed water used — depending on the source of the information. Prominent examples of agriculture reuse include the Cities of Orlando and Tallahassee in Florida. The system in Orlando is part of a joint program called Conserv II between the city of Orlando and Orange County, Florida.

Groundwater Recharge

Water Factory 21 in Orange County, California has been conducting reuse research and injecting effluent via wells into the coastal aquifer since 1976. WWTP effluent is combined with well water prior to injection. This indirect potable reuse has a psychological advantage in that there is a loss of identity between reclaimed water and groundwater. In Florida, the previously mentioned Conserv II program in Orlando also involves rapid infiltration basins for groundwater recharge.

Augmentation of Potable Supplies

Besides the indirect potable reuse just mentioned under the heading of groundwater recharge, direct potable reuse is also possible. There are major psychological barriers to this application although considerable research has been conducted in Denver, San Diego, and Tampa. Currently direct potable reuse is not practiced anywhere in the United States.

Environmental Enhancement

This category includes the use of reclaimed water for the creation or enhancement of wetlands, stream augmentation, and recreational and aesthetic impoundments. Examples of two major wetland enhancement systems to provide wildlife habitats as well as additional effluent treatment prior to discharge are sites at Orlando, Florida and Arcata, California. Other applications in this category include the creation of recreational lakes and snowmaking.

Industrial Reuse

In-plant recycling is an important part of many wet process industries. Separate from this, industrial applications of reuse (WWTP effluent) water include: evaporative cooling, boiler-feed water, process water, and irrigation of plant grounds (Goto, 1995). The cooling water application and the utility power industry are by far the predominant industry reuse situations.

To illustrate the practice of reuse, three examples of reuse studies are provided next.

Examples of Reuse Studies

To access the entire paper, click here.