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This paper presents a brief analysis of what water conservation means, why conservation is needed, when it is required, and how it should be accomplished.
It also reviews a number of studies being carried out in Portugal by the Laboratorio Nacional de Engenharia Civil (LNEC) which can serve as a useful basis for designing a water conservation policy for the country.
There is an ever increasing awareness that water resources, which are mobile, renewable natural resources, exist in limited quantities. Moreover, the available supply can vary considerably during the course of a year, as well as from year to year and from region to region. Thus, a continuous and indefinite expansion of water uses is not possible. A situation of stability in the use of the water that is currently available must be sought. This should be one of the main strategic goals of a long-term water management policy. There is an urgent need to find ways of saving, reusing and recycling water, and to develop methodologies to improve water resource management.
Water conservation may have different meanings for different people. It may remind us of the possibility of collecting rainwater in small tanks for domestic use, or constructing dams and reservoirs; of recharging groundwater tables, or using lower quality water whenever possible in order to save better water. Water conservation encompasses all this. It involves reducing the demand for water by fostering water conservation habits, stopping wasteful uses, decreasing peak consumption and charging for water at the appropriate rates. It also means taking advantage of technological developments and improved management techniques; coordinating water resource planning and management with land-use planning and economic and social planning; and establishing new or updated standards and regulations. In short, water conservation means optimal water use.
It should be stressed that except in drought or other exceptional conditions, a water conservation policy is not intended to enforce arbitrary cuts in water consumption levels at the expense of the quality of life of the population. Its main purpose is different: the efficient use of a limited resource which is essential to life.
The problem of water conservation in Portugal will undoubtedly become increasingly important. There is a growing need to improve water resource management in general, as well as the management of certain subsystems, particularly those relating to water supply and sanitation.
In 1985 an estimate of water availability and water demand for the years 2000-2020 was made and the respective balance was drawn up (Henriques, 1985).
The results showed that at the national level, the situation may be considered satisfactory, providing certain water quality problems can be adequately resolved.
There are, however, problems at the regional level, owing to the uneven distribution of available water resources in different areas and at different times of the year. The areas where water supply is a major factor upon which economic activity depends are the catchment basins of the Sado and Guadiana rivers in southern Portugal, the Algarve region, the river Mira watershed, both also in the south, and the Estremadura region in the central region of Portugal.
Although in recent years the development of public water supply and sanitation services may be regarded as positive, these services are still a long way from being acceptable, with marked differences in quality across the country.
In 1987, an average of 62.5% (varying between 90% and 24% in the various administrative districts) of the population in Portugal was served by a water supply system (Silva, 1990). In that same year, the percentage of the population with access to public sewerage systems was 42.3% (varying between 80% and 13% in the various districts); and wastewater treatment plants served only 11% of the population (varying between 41% and 4% in the various districts).
According to a study carried out by Baptista and Correia (1989), the amount of investment required to upgrade public water supply services and rehabilitate existing systems (ensuring that 95% of the population would be connected to supply networks), would be about one billion US dollars (1989 estimate). The amount needed to reach the same goal for sewerage systems is undoubtedly far higher.
Consequently, the need to make efficient use of existing water resources and optimize the investments required means that special attention should be paid to the topic of water conservation, which should be supported by the appropriate research and development activities.
A 1983 paper presented at the Laboratorio Nacional de Engenharia Civil (LNEC), in Lisbon, Portugal (Bau, 1983) outlined the current state of water conservation, with special emphasis on water supply systems for large urban centers. It identified many pending problems that needed to be studied in Portugal and presented specific programs for dealing with some of those problems. A few of the points brought up in the above-mentioned paper are referred to in the following section.
Water supply systems are planned, programmed and constructed with the aim of meeting future water demands.
Consumption forecasts at the design stage of water supply projects will condition the type, dimensions and long-term scheduling of the works, and thus the amount of investment required.
The evolution of demand should be studied not only with a long-term perspective; short-term demand projections can also be very useful in planning the operation of a water supply system, and for studying the economic and financial equilibrium of water supply services.
Most conventional methods of forecasting the evolution of demand are based on studies of population growth, per capita and per diem water consumption coefficients, and peak factors (ratios between mean consumption and maximum consumption per hour, day, week, or year). However, long-term water demand forecasting systems should take into account a wider range of factors in order to produce the data needed for planning and programming the construction of supply systems. Models and rates of economic growth are undergoing substantial changes in many regions; the size and type of housing are evolving; economic incentives in water resources management, such as payment of rates for water outlets and for disposal of effluents are finding increasing acceptance; and water conservation policies are more and more likely to be adopted. There is therefore a need to study methodologies that make it possible to forecast the evolution of water consumption in a given supply system.
Improving the management of water demand in a supply system, however, is not restricted merely to using improved or more advanced methodologies for studying the evolution of consumption. A new perspective should be taken into account: that the evolution of demand should not take place in an uncontrolled manner, without this being in any way dependent on the will of those responsible for water supply services. The demand for water is conditioned to a certain extent by the policies adopted by those in charge of the supply system, and nowadays they cannot ignore the possibility of influencing water demand and supply. Planning the evolution of water supply systems should not only envisage the adoption of “structural measures” based on the construction of new works. The management and planning of such systems should also consider the use of “nonstructural measures”, and special attention should therefore be paid to the problem of water conservation.
A number of reasons have been put forward to justify a water conservation campaign within the scope of a water supply system. The most common of these (for details see Bau [1983]) are the following:
b) improving the operation of existing water supply systems;
c) postponing investment in water facilities;
d) reducing energy consumption:
2. energy saved in use, taking into account that part of the water used is heated;
3. energy saved in operating drainage and wastewater treatmentsystems as a result of decreased sewage disposal;
e) reduced disposal into sewerage systems;
f) pressure of public opinion.
An effective water resources management policy entails the adoption of water conservation measures at both supply and consumption levels.
As regards supply, conservation is achieved by making better use of the available water resources and by measures aimed at increasing those resources, as well as by actions to improve the efficiency of supply systems, such as replacement and repair of old pipelines, proper control of pressures in the network, leakage repair, and reduction of losses in water treatment plants.
Water conservation at the user level includes public education and public information programs, rate structure policies, and the drafting of legislation, such as regulations governing specifications for domestic water fixtures, obligatory installation of low-consumption devices, watering of private gardens, strict control of sources of pollution, treatment of effluent, and recycling and reuse of wastewater.
Technological developments in various fields have also provided the means to reduce water consumption. Examples include low-consumption devices (toilets, showers, faucets, washing machines and dishwashers, etc.), parks and gardens requiring little watering, use of recovered water (from treated wastewater) for watering parks and gardens, use of mechanical street-cleaning methods, and introduction of industrial technologies with low water consumption.
It should be pointed out that in every case, the characteristics, advantages, drawbacks and limitations of any potential measure should be carefully considered, and the specific conditioning factors, in terms of time and place, of the supply system concerned should be taken into account.
Reference is made below to a number of studies being conducted at the LNEC which may be of interest in designing water conservation programs and developing methodologies for forecasting the evolution of consumption.
The first of these studies introduced a methodology that makes it possible to inventory water use and actual water consumption in the industry of a given region, based on a survey of different industrial plants. The techniques developed were applied in a study of water use in the Ave river basin in northern Portugal (Santos and Bau, 1984).
The survey was carried out on a sample of 110 industrial plants, selected in such a way as to represent the industry of that region as accurately as possible.
For several industrial activities it was possible to obtain mean water use coefficients per production unit and per worker. In many cases those coefficients showed values that were at variance with those found in the literature.
A second study currently under way at LNEC concerns the analysis of urban water demand profiles. According to Alegre (1988) this study has four main purposes: a) definition and development of methodologies for measuring, recording, processing, filing and forecasting consumption data; b) obtaining diagrams of daily variations in consumption for a set of diverse situations; c) determination of the factors that most influence domestic consumption and definition of the existing ratios, and d) development of consumption forecasting techniques.
Several study areas with similar characteristics were selected. In the first stage, eleven study areas in the municipality of Almada, in the center of the country, near Lisbon, were chosen. These included residential districts with different socioeconomic standards and various types of housing (apartment blocks, villas, terraced houses, etc.), commercial/residential areas and seaside resorts. Three additional areas in Vilamoura (Algarve), in southern Portugal, were selected during the second stage. A further three areas in the north of the country are to be analyzed in later stages of the study.
This project is expected to result in a set of software tools to put the above methodology into practice, basically by inputting urban characteristics and outputting load profiles and statistical distributions.
The third study is on the reuse of wastewater treated for irrigation purposes. During the past five years LNEC has been conducting an experimental study in two wastewater treatment plants (Evora and Santo Andre-Sines) in Alentejo, in southern Portugal. The purpose of the study is to define methodologies for the use in agriculture of wastewater treated by various processes, draw up a balance of the benefits and disadvantages associated with this kind of reuse, and make the most effective use of the treated water.
Effluents treated by three processes - primary sedimentation, secondary sedimentation after high-rate trickling and facultative pond - were tested by furrow and drip irrigation of three crops - a forage crop (sorghum), a cereal (maize) and an oilseed (sunflower). For purposes of comparison, the same crops were irrigated with potable water and given commercial fertilizers.
According to a study by Marecos do Monte and Sousa (1991), the yields of crops irrigated with primary and secondary effluents were very similar to those irrigated with potable water and provided with commercial fertilizers. Furthermore, the observed yields were very close to the theoretically expected yields.
The similar crop yields obtained with the three types of treated water indicate that the nitrogen content of the sewage effluents has a fertilizing value similar to that of commercial fertilizers if treated wastewater is used for irrigation.
In general there appeared to be no adverse effects on crop composition after irrigation with primary and secondary effluents.
The results show that contamination levels in crops that are gravity irrigated with treated effluents (primary and secondary treatment) are similar to those for the same crops irrigated with potable water. A possible explanation for the higher level of fecal coliforms in sunflower irrigated with primary effluent evidently lies in reasons extraneous to the irrigation water used (feces of birds on the seeds; aerosol deposits in primary effluent from the rotary distributor that feeds the percolator bed; bacteria carried onto the plants by ants and other insects) rather than in its own contaminating potential, since this did not occur in the case of sorghum.
Soil contamination was assessed by comparing the quantity of fecal coliforms present in soil samples before planting the crops and after the irrigation cycle. The results show that soil contamination is negligible forty days after the conclusion of irrigation.
Following the experience obtained in Portugal, the LNEC, in collaboration with other institutions, prepared a research program with a view to studying wastewater performance in an African country with a major shortage of water - the Republic of Cape Verde.
The wastewater used comes from the Ribeira da Vinha wastewater treatment plant (lagooning system), which receives effluents from the town of Mindelo. The effluent, which has high salinity, will be used to irrigate at least three crops, using three irrigation methods (gravity, microspray and drip).
The main aims of the study can be regarded as an experimental evaluation of tolerance in the use of effluents with medium and high salinity for irrigating crops of economic interest to the region, comparison of the efficacy of the various irrigation methods with an effluent rich in microalgae, and evaluation of the sanitary risks involved in using an effluent, owing to pathogenic agents and toxic chemical elements (mainly heavy metals).
ALEGRE, H., “Estudo dos diagramas de consumo de água urbano”, Encontro Nacional de Saneamento Básico 88, APESB, Lisbon, 1988.
BAPTISTA, J. M. B. and CORREIA, F. N., “Qualidade das águas destinadas ao consumo humano. O impacto da directiva comunitaria em Portugal”, Proc. SISIPPA 89, Vol I, Lisbon, 1989, pp. 129-145.
BAU, J., “Gestão da procura em sistemas de abastecimento de água a aglomerados urbanos”, LNEC, Lisbon, 1983, 225 p.
CESL, “Estudo das condições de utilização da agua na industria”, CESL, Lisbon, 1981.
COELHO, S. T. and ALEGRE, H., “Demand analysis in water supply and distribution systems”, LNEC, Lisbon, 1988.
HENRIQUES, A. G., “Avaliação dos recursos hidricos de Portugal Continental”, I.E.D., Lisbon, 1985, 151 p.
MARECOS DO MONTE, H., “A reutilização de águas residuais tratadas para rega - um contributo para o combate a desertificação” Jornada sobre desertificação, CCRA, Evora, 1988.
MARECOS DO MONTE, M. H. and SOUSA, M. E. S., “Irrigação do milho, girassol e sorgo com efluentes de tratamento primãrio e secundario de águas residuais urbanas”, II Seminario Luso-Espanhol de Estruturas Rurais, Madrid, 1991.
SANTOS, M. A. and BAU, J., “Utilização da água na industria. Inquérito na bacia hidrografica do Rio Ave”, Report 241/84 NHHF, LNEC, Lisbon, 1984.
SILVA, J. M. M. D., “Niveis de atendimento da população portuguesa com servicos de agua, esgotos e lixos. A situação na Europa. Custos de aproximação à CEE”, GEPAT, Lisbon, 1990.
THACKRAY, J. E. and ARCHIBALD, G. G., “The Severn-Trent studies for industrial water use”, Proc. of the Institution of Civil Engineers, Part 1, No. 70, London, August 1981, p. 403-432.
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