Document(s) 10 of 14

Factors affecting demand for water

The purpose of any water supply system is to satisfy the needs of communities. The suitability of any water resource to meet the demand hinges on the specific requirements of the communities that will use it.

The amount of water consumed by a community depends on many factors. External factors include climate: more water is needed in hot weather than in cold. Some factors may be cultural, e.g., the restriction on water during Ramadan in Muslim countries, or behavioural, e.g., washing practices. These patterns are not unrelated to water availability, but they do not necessarily reflect the level of actual or potential supply. For instance, although hot weather during the summer season tends to increase demand, requirements may actually decrease if most people go on vacation during that period. This situation is often found on hot summer weekends in cities; the fewer people in town compensate for increased consumption per person.

Water demand also depends on water availability. People adapt to available volume and, although there is some inertia involved in modifying habits, increasing supply volumes usually produce some increase in consumption level (other factors being equal). This is probably one of the reasons why the rate of consumption is high in Buenos Aires, i.e., proximity to the large fresh water Río de la Plata (another reason is the lack of metering).

The single most important factor affecting water demand is the existing infrastructure for its supply, i.e., conduction, treatment, storage, and distribution systems. A key element is the ratio of service connections to the number of households. Households without connections normally (but not necessarily) consume much less water, and consumption per person increases with the number of connections. In Latin America, the number of new connections lags behind the number of new households, especially in the fastest growing cities in the poorer countries (Lima, Managua, and Port-au-Prince).

Leakage of water from the distribution systems artificially inflates the rate of consumption. Although leakage occurs in any system’ On the order of 10–20% of the water in the system), in obsolete systems this proportion can increase to 30–40% or more, e.g.,

in Lima and Recife, leakage is estimated to be as high as 50%. As discussed in Chapter 9, this problem is serious in Latin America and the Caribbean (LAC) at this time of budgetary restraint. It would be difficult to find any large city on the continent not experiencing this problem. In some cities, leaked water is lost; in others, it finds its way into aquifers and may be at least partly retrieved (at a cost), as is the case in Lima.

Policies of the water management authorities can be used to regulate use as well. Metering and pricing policies are probably the most important in affecting consumption and demand. Water companies should ask themselves a number of questions:

• Is there adequate control (metering) of consumed water?
• Are pricing policies equitable for all neighbourhoods?
• What are the policies for different uses (domestic, industrial, agricultural, etc.)?
• Does cost differ with different levels of consumption?
• Are there different prices for peak periods? and
• What policies address leisure use of water, e.g., swimming pools and watering gardens?

Finally, the technological efficiency of water use can affect demand. Appliances and fixtures designed to provide water are a factor to be considered. To a large extent, “water-using technology and not the user’s behaviour, determines the amount of water used” (Brooks and Peters 1988). In Latin America, most water-using appliances are copied from models used in developed countries. In most cases, regulations and controls of appliance efficiency are absent, inadequate, or not enforced. (Recently, new policies have been introduced in some countries, e.g., Mexico, where 7-L flush toilets have been promoted as replacements for 20-L ones.)

In spite of the importance of reducing unnecessary or wasteful water consumption, little is done in this regard. Although water can be expensive for people at the lower income levels, the price charged to consumers is still below the cost of supplying it when capital investments, maintenance, and other expenses are considered. Well-off urban residents of the LAC region take for granted their access to large volumes of water at a low cost, even when wasting water may mean inadequate supply to less-affluent neighbourhoods. In Lima, “leisure lakes” are fed through the municipal La Atarjea system, while more than 300 000 households have no service. However, wastage is not an exclusive practice of the urban upper classes; waste occurs throughout the social spectrum, including the urban poor.

Water is a valuable resource and its true economic worth must be recognized by decision-makers and consumers alike. Only with this awareness will it be possible to bring demand levels in line with the actual and reasonable needs of the populations.

Level of demand in Latin American cities

Consumption levels in Latin American cities vary from slightly more than 100 L/day per person to more than 500 L/day (Table 4). These figures include total demand from the water company divided by the population. However, in many cases, they also include industrial or agricultural usage, obtained from the municipal service but not always computed as such. In some cases, they do not include considerable volumes of water obtained from domestic wells.

Table 4. Municipal water consumption and wastewater production in large metropolitan areas of Latin America.

However, water demand cannot be measured only by the level of consumption. Consumption is always below potential demand because of interruptions to the service, low pressure, insufficient connections, etc. On the other hand, if conservation measures were applied, consumption could be significantly reduced. Methods to bring about a reduction include:

• Reducing leakage to eliminate up to 20–30% of false consumption;

• Introducing water-saving technology, such as smaller toilet tanks and low-volume shower heads; and
• Changing water-consumption patterns, e.g., through adequate pricing policies or voluntary life-style changes, to stop wasteful practices or decrease consumption during peak periods (systems are overdesigned to meet infrequent but critical peak loads).

Actual consumption could be reduced by more than 50% in many LAC cities, simply through adequate maintenance, appropriate policies, and greater public awareness. Conservation alone could probably compensate for current deficits and a portion of future expansion in many cities of the region for a few years. However, conservation efforts cannot bring more water into the systems. There is still a need to protect present water sources and find new ones, both natural and artificial, i.e., recycled wastewaters.

Water resources and the use of wastewater

Water systems include inputs (e.g., natural sources and used water), the system itself, and outputs resulting, directly or indirectly, from the functioning of the system (e.g., water for recreation, homes, industries, and irrigation and electrical energy) (Sewell and Bawer 1968).

Inputs

Although the primary input (natural water sources) has been dealt with extensively in this publication, the potential of wastewater as an input has been only briefly mentioned. Its importance cannot be overestimated, as has been shown in same countries of the Middle East, such as Israel and Jordan. In the LAC region, used water is considered a problem rather than a resource. It is usually disposed of after little or no treatment, with the result that streams and other water bodies near cities are highly polluted. Currently, some use is made of wastewaters for irrigation, e.g., in Mexico and Peru. The Tietê River near São Paulo and the Mapocho River in Santiago, both of which contain considerable amounts of waste, are used for irrigation and by industries.

The amount of water used for irrigation and industrial purposes in most countries is larger, sometimes by an order of magnitude, than the amount used domestically; The quality standards for this water are frequently less strict than those for drinking water or other domestic uses, although some types of irrigation require water of high quality. Industrial water standards can vary substantially. Some processes require pure water or water with specific characteristics. However, in other cases, industrial water may be relatively impure and even contaminated without affecting its use, e.g., water for cooling machinery. Some of these requirements can be met by reusing wastewater. With effective treatment, wastes can even be turned into good-quality drinking water.

Although plants that treat water for reclamation are more expensive to build and operate than more common treatment plants, the additional costs are often lower than those needed to develop new water resources. Reclamation plants differ from normal treatment plants in several ways (Okum 1990):

• Their location is more influenced by the “market” for reclaimed water;
• The sludge can be disposed of elsewhere and even returned to the sewage system;

• The volumes reclaimed can be geared to need, i.e., it is not necessary to treat all the water; and
• The product is sold and, therefore, must be reliable in terms of quantity and quality.

In the United States, several water-reclamation systems have been in operation almost from the beginning of this century: Baltimore’s Back River plant (1942) and Grand Canyon Village in Arizona (1926), which has a dual system for potable and nonpotable output. In the Irvine Ranch Water District, the cost of reclaimed water was found to be one-third less than that of water from the usual system.

Reclamation of used water has also been initiated in Israel, Singapore, the petroleum--producing countries of the Middle East, and some islands of the West Indies. Other examples can be found in the Beijing-Tianjin area in China, which started operation in 1988, and North Africa. Studies are under way in São Paulo to explore the possibility of reusing water from a secondary treatment plant for industry.

Water reuse is gradually going to gain importance as a source of nonpotable water. Dual systems are a potential tool for better water use in countries where the risk of misuse is high. In any case, developing countries and particularly urban areas of the LAC region cannot afford to ignore this resource, which often represents the best option for meeting the crucial need for more water.

The system

Water systems are designed to obtain water from a natural or artificial source and deliver it to the various users. Normally the water macrosystem includes:

• A regulating system at the source, Le., a system of dams for storage and regulation of stream flow;
• An intake system, i.e., dams, pumps, canals, and various pools, which may also include a conduction system leading to the treatment plant;
• A treatment system, i.e., filtering, sedimentation, and chemical-treatment pools and canals, and pumps;
• A conduction system from the treatment plant to the consumption areas;
• Various storage structures, almost always near the consumption sites, but also in intermediate locations; and
• A distribution system, Le., a network of pipes and canals, pumps, associated storage structures, and household connections.

Because of the complexity of water management in urban areas, water systems require material, technical, economic, administrative, and legal support for everyday operation. In addition, they require continuous monitoring and maintenance as well as heavy investment in replacements for obsolete elements and expansion. In the LAC, this support is normally provided by one or more public enterprises, although in several cases services have been provided by a private company.

Outputs

The main output of the system should be water in a condition that is compatible with its destined use: drinkable water for homes; water with various levels and types of dissolved solids for industries; and uncontaminated water for irrigation and leisure use.

However, this is not always the case in the LAC region. The potability of the water is often doubtful due to contamination of the sources and inadequate treatment. In many cases, monitoring of quality is unreliable. In many cities, the concentration of heavy metals and toxic organic material is not monitored properly.

Economic analysis

One of the key problems in the evaluation of any proposed method or scheme for urban water supply is the relation between expected results and estimated costs. Although, the calculation of costs should be a relatively straightforward exercise if all necessary scientific and engineering information were available, this is often not so. Hydrological and hydrogeological investigations are essential before decisions about alternative methods of water supply can be made.

Other important factors must also be considered to balance the various possible options. One of these is the ability of governments and communities to pay for construction, operation, and maintenance. It is also important to fit water projects into urban-planning strategies. However, we are concerned not only with water and engineering issues, but also with the environmental, social, political, and administrative aspects of the problem. Factors that must be carefully evaluated before an urban water-supply project is supported include:

• The current situation, i.e., present consumption; population; breakdown of household, industrial, commercial, and institutional consumers; number of connections and public standpipes; unsupplied consumers; presence of gardens and swimming pools; and number of breakdowns, leakage, and disruptions;
• Environment and geography, i.e., climate, area covered by the water service, topography, and seismicity;
• Cost of exploration, identification, and characterization of the water source (most research costs are included here);
• Cost of induced or artificial recharge of aquifers;
• Cost of water-extraction structures;
• Cost of water-treatment facilities;
• Cost of water-conduction structures;
• Cost of storage structures;
• Cost of distribution networks, including metering devices; Cost of operating and maintaining all equipment;
• Cost of lost water resources (for other purposes or for other communities);
• Cost of fisheries affected (if any);

• Environmental cost;
• Other environmental effects (short- and long-term, positive and negative);
• Effects on job creation or elimination;
• Other social effects, both positive and negative; Availability and cost of credit or funding;
• Ability of communities or governments to pay all of these costs; Technical feasibility of the project;
• Availability of qualified personnel to carry out the work and operate the installations;
• Administrative and political framework to manage the scheme during construction and operational phases;
• Future demand, according to expected growth of the population and the system’s ability to expand; and
• Ease of access to water by different socioeconomic groups, in the volumes that are needed and at the required pressure.

Along with the analysis of costs, a qualitative assessment of the benefits can be carried out. Convenience, reliability, accessibility, health advantages, and increased social productivity (through reduction of the time required to obtain the water) should all be measured.

This checklist applies to specific projects designed to solve well-defined problems or to take care of specific needs after the main research issues have been addressed. In projects involving unknown elements, scientific research is required before a complete assessment of these factors can be carried out. However, to implement the results of the investigation successfully, these issues should be kept in mind and an economic evaluation provides a good starting point for comparing various options.

Economic evaluations of water projects must be carried out in a global context. Included in the bill will be the cost transferred to future generations if the environment is damaged, and the ethical aspects of distribution of the resource among the different social groups, sectors, or classes. (Updated information on administration of water resources in Latin America and the Caribbean can be found in ECLAC (1991).)

Document(s) 10 of 14