Applying water quality indexes ( WQI ) to the use of water sources for human consumption

Naturally occurring and anthropic contamination of water sources limits the use of water for human consumption. Fast and representative tools, such as water quality indexes (WQI), allow performing an integral assessment of the resource, this being essential when making decisions about the management and control of sanitary risks through different purification processes. A comparative analysis of applying WQINSF, Dinius WQI, ICAUCA and UWQI indexes at five points or stations on the Cauca River located in the Salvajina–Puerto Mallarino water uptake section, gave evidence of growing river deterioration due to the different socio-economic activities carried out in the river basin. This water quality condition brings about the incorporation of additional or specific treatment operations such as activated carbon or adsorption for the destination of the resource for human consumption. The presence of pathogens and particulate material were the variables mostly affecting WQI value. It is thus recommended that the development or adaptation of an index having a similar structure to the DQWI index should be considered to make a thorough river assessment and the additional use of soil which might generate the presence of other substances causing a sanitary risk in the source, considering variation in time and space of the parameters comprising it and its comparison with current legislation.

De manera más reciente se han planteado ICA para la evaluación del recurso hídrico a ser destinado al consumo humano, previo tratamiento, que incluyen parámetros fisicoquímicos y microbiológicos relacionados con el nivel de riesgo sanitario presente en el agua, como el ICA para abastecimiento público -IAP de Brasil (CETESB, 2006), el Universal Water Quality Index -UWQI (Boyacioglu, 2007), basado en Directivas de la Unión Europea, y el Drinking Water Quality Index -DWQI, de la UNEP (actualmente en revisión (UNEP, 2007)) El índice IAP considera parámetros que requieren técnicas de medición con límites de detección muy bajos que cumplan con las especificaciones para su cálculo, y el DWQI presenta una estructura de cálculo fundamentada en la variación en el tiempo y en el espacio de los parámetros que lo conforman y su comparación con la normatividad vigente de acuerdo con el uso estudiado, lo cual puede favorecer la evaluación de fuentes con amplias variaciones de calidad en el tiempo y facilitar su aplicación a las condiciones particulares de una región o país; sin embargo, su cálculo requiere información de todos los parámetros que lo conforman, colectada a lo largo de un periodo de tiempo -usualmente un año- (Torres et al., 2009).En Colombia el deterioro del recurso hídrico se debe principalmente a vertimientos de aguas residuales domésticas, industriales y agropecuarias, y actividades como transporte terrestre, fluvial y marítimo de sustancias peligrosas o petróleo, aguas de extracción minera y residuos sólidos dispuestos en rellenos sanitarios o directamente en éstos (Ideam, 2001).A pesar de que en promedio el 78% de la población tiene acceso al agua potable (Andesco, 2008), en algunos departamentos existen problemas de calidad del agua para consumo humano (Álvarez, 2008).El río Cauca es la segunda fuente de mayor importancia del país, ya que un 25% de la población se ubica en su área de influencia, localizandose en su cuenca 183 municipios de los departamentos de Cauca, Valle del Cauca, Quindío, Risaralda, Caldas, Antioquia, Córdoba, Sucre y Bolívar (Ideam, 2001).En este río se han aplicado o -In English ploitation, due to the alteration of the physicochemical, microbiological and parasitological characteristics determining the complexity and costs of the treatment required for making water suitable for human consumption.One of the principles guiding water supply is the concept of multiple barriers involving source protection and optimisation of processes in water treatment plants and suitable distribution system management (Betancourt and Rose, 2004) Raw water assessment must consider representative indexes guaranteeing integral analysis of water resources and allow action to be taken for management and control through different water purification processes.One of the most widely used tools is the water quality index (WQI).Such indexes lead to identifying tendencies related to changes in water quality and environmental specifications, helping governmental decision to be made and assessment of control programmes (Ott, 1978;Canter, 1998).
Indexes have been developed worldwide.One of the most widely known is the National Sanitation Foundation Index (WQI-NSF) which was developed by Brown et al., (1970) for United States rivers and has been applied and validated in several international studies.Dinius (1987) proposed a similar WQI, but suggested classification ranges based on specific uses apart from human consumption.
More recently, several specific WQI for assessing water resources intended for human consumption after treatment have been suggested and these include physicochemical and microbiological parameters related to the level of sanitary risk present in the water.Some examples are the WQI for public supply (IAP) in Brazil (CETESB, 2006), the Universal Water Quality Index (UWQI) (Boyacioglu, 2007) based on directives by the European Union and the Drinking Water Quality Index (DWQI) by UNEP (currently in review (UNEP, 2007)).
The IAP index considers parameters that require measurement techniques with detection limits too low to satisfy calculation specifications and the DWQI presents a calculation structure based on variation in time and space of the parameters comprising it and a comparison with current legislation according to studied use, which can favour the assessment of sources having wide quality variations in time and facilitating its application to the particular conditions of a region or country.However, the calculation requires information on every aspect of the index, collected during a long period of time (usually a year) (Torres et al., 2009).
The deterioration of the water resources in Colombia is mainly attributed to domestic, industrial and agricultural wastewater discharges and activities such as terrestrial, fluvial and maritime transport of hazardous substances or oil, mining extraction water and solid residue disposed of in sanitary landfills (IDEAM, 2001).Even though around 78% of the population has access to potable drinking water (ANDESCO, 2008), water quality issues regarding human consumption still prevail in some departments (Álvarez, 2008).The Cauca River is the second most important water source for the country, as 25% of the population is located in its area of influence, including 183 municipalities in the basin spread over several departments: Cauca, Valle del Cauca, Quindío, Risaralda, Antio-En español adaptado ICA de amplio uso internacional; Rojas (1991) adaptó el ICA-NSF a las condiciones específicas del río, enfatizando su uso para consumo humano previo tratamiento, y la Corporación Autónoma Regional del Valle del Cauca -CVC-y la Universidad del Valle (2004) adaptaron un ICA a partir de los ICA NSF, Dinius, CETESB e ICOSUS, denominado ICAUCA.En este documento se hace un análisis comparativo de la aplicación de diferentes ICA para la evaluación de la calidad del agua del río Cauca como fuente de abastecimiento para consumo humano previo tratamiento, en el tramo Salvajina -Bocatoma Puerto Mallarino, y su injerencia en la toma de decisiones relacionadas con su viabilidad de uso para potabilización.
In English quia, Córdoba, Sucre and Bolívar (IDEAM, 2001).Several widely used indexes have been applied or adapted to this river.Rojas (1991) adapted the WQI-NSF to the specific river conditions with special emphasis on water for human consumption following previous treatment and CVC and Universidad del Valle (2004) adapted a WQI from the WQI NSF, Dinius, CETESB and ICOSUS indexes, which was called ICAUCA.A comparative analysis is made in this work of applying different WQI for assessing the water quality of the Cauca River as a supply of water for human consumption after treatment, in the Salvajina-Puerto Mallarino water uptake section and the influence on making decisions related to the viability of water use for purification.

Methodology Sampling and source characterisation
The definition of the section and 5 sampling points or stations on the Cauca River was based on criteria relative to the pattern of historical information regarding water quality in this section and localisation on the main tributaries discharging into the river.WQI assessment was based on the information collected from 3 samplings carried out at 5 selected points during a 9-month period to characterise different weather and river quality conditions.Each sampling point involved 3 samplings taken in the transversal section of the river at each point, except for dissolved oxygen and coliforms for which instant samples were taken in the middle point of the section.
Figure 1 shows the location of the selected sampling points and Table 1 shows the measured parameters and the analysis techniques considered according to APHA et al., 2005.

Water quality indexes
Based on a literature review and some known basic characteristics of the section to be studied, four WQI were selected according to the following criteria: broad application at international level, classification considering the destination of the resource for public supply and being representative of the study's local conditions.
Table 2 shows the selected WQI with their respective calculation equations and some observations related to the equations. Estimación de los subíndices "Ii" que corresponden a la transformación adimensional de cada parámetro que conforma los ICA mediante curvas o ecuaciones matemáticas.Los valores de "Ii" varían entre 0 y 100, cuanto mayor es Ii mejor es la calidad del agua. Asignación del peso relativo (Wi) que define la importancia de cada parámetro dentro del ICA evaluado y se relaciona con el uso a evaluarse; la sumatoria de los pesos "Wi" debe ser igual a 1. En estos índices en general, los parámetros que tienen mayor peso relativo son el oxígeno disuelto, los coliformes y los asociados a presencia de materia orgánica como la DBO.La Tabla 3 presenta los pesos asignados a los parámetros que conforman cada ICA. Finalmente, con los valores de "Ii" y "Wi" obtenidos en cada caso, se realizó el cálculo de los ICA seleccionados.

WQI was calculated by means of a series of stages:
 Estimating "Ii" sub-indexes corresponding to non-dimensional transformation of each parameter forming the WQI by means of curves or equations."Ii" figures varied between 0 and 100, the higher the figure the better the water quality;  Assigning the relative weight (Wi) defining the importance of each parameter in the assessed WQI and its relationship to the use to be evaluated; the sum of all weights must equal 1.As a general rule, the parameters having the highest weight were e dissolved oxygen, coliforms and those associated with the presence of organic matter such as BOD.Table 3 presents the assigned weighting for the parameters comprising the WQI; and  Calculating the selected WQI from the values obtained for "Ii" and "Wi" in each case.
En cuanto al comportamiento de los patógenos, los niveles de coliformes totales y fecales evidencian la problemática que presenta el río a partir de la estación 2, con valores que superan los niveles reglamentados para aguas a ser destinadas al consumo humano previo tratamiento convencional, lo cual incide directamente en el nivel de riesgo agudo presente en sus aguas, aspecto que es determinante en el suministro de agua segura a la población y hace prioritario su control en los sistemas de tratamiento de agua abastecidos por la fuente.Como respuesta a esta problemática, actualmente en las plantas de la ciudad de Cali que se abastecen con esta fuente se aplica pre y poscloración como medida de control del riesgo microbiológico.

In English
As observed in the above Table, the physicochemical characteristics were below established limit values excepting for phenols which were above them (0.002 mg/L) in the studied section of the river.Such high phenol concentration makes additional water treatment necessary and purification plants in the city of Cali have implemented activated carbon dust adsorption (CDA) to reduce the presence of phenol compounds in the river water (Torres et al., 2008).
The characteristics of the sampling ports allow identifying three sectors: Sector 1: Salvajina dam -Station 1: had figures similar to those usually reported for good quality superficial sources, associated with settling phenomena and dilution in the Salvajina dam and not much influence of domestic or industrial wastewater discharges.
Sector 2: Station 1-2: an increase in suspended material and pathogen levels was observed that affected river water quality.This increase could be attributed to wastewater discharges originating from population settlements along the river as well as the contribution of particulate material from the Ovejas and Timba rivers.
Sector 3: Stations 2 -5: presented characteristic values for surface water having notorious water quality deterioration associated with increased agricultural, industrial and urban activities in the sector.The Hormiguero station registered the highest values of suspended solids, turbidity and apparent colour, possibly due to the influence of the Palo, Zanjón Oscuro and Jamundí rivers which present issues related to erosion in their basins.
An important aspect, which must be pointed out, was the high COD and low BOD levels characteristic of low organic contamination (<2 mg/L - UNESCO, 1996).This condition could indicate that inorganic oxidable substances are being discharged into the river, thereby increasing COD concentration and could negatively influence the chemical risk present in the river.
Regarding pathogen behaviour, total and faecal coliform levels were well above the limits for water intended for human consumption after conventional treatment after Station 2 which directly influences the level of acute risk present in the water and is determinant in the supply of safe water to the population.This makes controlling the treatment systems supplied by the source an urgent priority.Purification water plants in Cali which are supplied by this source have implemented pre-and post-chlorination as a microbiological risk control measure to deal with this situation.
Comparing the results obtained here with previous studies by CVC and Univalle (2004) it was observed that the figures presented in the section being studied are characteristic of the river, mainly during winter and transition weather conditions in which the river has increased dilution capacity.This was reflected in the low concentration of parameters such as BOD and high OD levels.The contrary occurred for parameters associated with the presence of particulate and dissolved material (total suspended solids, turbidity, En español rente, hierro y manganeso), los cuales aumentan debido a un mayor arrastre de materiales del suelo y del lecho del río.
Se resalta que durante los muestreos no se presentaron eventos extremos de contaminación asociados principalmente a niveles de OD inferiores a 2 mg/L o turbiedad superior al valor límite establecido para tratabilidad del agua por las plantas de la ciudad de Cali abastecidas por el río Cauca (3.000 UNT), que se presentan eventualmente a la altura de la Bocatoma de Puerto Mallarino afectando la continuidad del servicio de suministro de agua a cerca del 80% de la población de la ciudad de Cali debido a la suspensión en los procesos de potabilización (Univalle y EMCALI, 2009).Durante el mes de febrero de 2009 las fuertes lluvias presentadas en la cuenca del río Palo ocasionaron derrumbes y empalizadas, aumentado los niveles de turbiedad en el río Cauca a valores hasta de 10.000 UNT a la altura de la Bocatoma de Puerto Mallarino.
En general, los ICA evaluados reflejan el deterioro en la calidad del agua del río, especialmente en las estaciones 3, 4 y 5, que están fuertemente influenciadas por vertimientos de origen doméstico, industrial y agrícola, ya sea de forma directa o a través de sus ríos tributarios, siendo las variables de mayor incidencia los patógenos y las asociadas a presencia de material particulado.Igualmente, los valores obtenidos por los ICA estudiados presentan un comporta- In English apparent colour, iron and manganese) which have increased due to soil material drag and the river bed.
It should be noted that there were no extreme contamination events during the sampling period ( mainly associated with OD levels lower than 2 mg/L or turbidity higher than the limit value established for water treatment in the treatment plants of the city of Cali which are supplied from Cauca River, i.e. 3000 UNT).Such high turbidity events eventually take place in the surroundings of Puerto Mallarino water uptake and affect the continuity of water supply to nearly 80% of the population of the city of Cali due to purification delay (Univalle and EMCALI, 2009).Strong rains falling in the Palo River basin produced landslides and bank erosion during February 2009, thereby increasing Cauca River turbidity levels to 10,000 UNT in the Puerto Mallarino water uptake section.

Applying water quality indexes
Figure 2 shows the average pattern for the WQI being assessed.It was observed that according to WQI-NSF, the river had good quality at station 1, regular quality at station 2 and poor quality at the rest of the stations which reported the lowest figures (39-55).This classification agreed with that for the 3 previously described sectors.
ICAUCA had a similar tendency to WQI-NSF, However, according to the established classification ranks for this index, the river had good quality at stations 1 and 2 (70-60) and acceptable quality at stations 3, 4 and 5 (40.6-41.9).It was also noticed that ICAUCA assigned an important relative weight to the group of parameters related to the presence of particulate material in suspension (a problem mainly associated with the basin during winter); the classification was similar to other assessed WQI.
The Dinius WQI indicated that river water required treatment for human consumption at all stations.However, with increased waste water discharge into the river in its trail, the index decreased and this influenced complexity and treatment costs.As with the WQI-NSF and ICAUCA, the lowest values were presented at the last 3 stations in the section being assessed.
The UWQI was not assessed at the Suarez station as no information on all the parameters required was available for making calculations.Although this index includes parameters related to chemical risk in the water due to the presence of selenium, arsenic, cyanide, cadmium and fluoride, the obtained results did not show these parameters' strong influence on the final value and classify the river as having regular quality throughout the studied section.This situation could indicate that the river presented a low chemical risk associated with sanitary interest substances considered by the index; however, for a thorough and integral assessment of the risk, the possibility of adapting an index must be considered which includes other substances being dumped which are related to the socio-economic activities predominating in the basin such as pesticides, phenols and other metals.
The assessed WQI reflected the deterioration of river water quality, mainly at stations 3, 4 and 5, and this deterioration was strongly influenced by domestic, industrial and agricultural wastewater discharge, directly or through tributary rivers.The variables that affected water quality the most were pathogens and those associated with the presence of particulate material.Also, the values obtained for the assessed WQI were quite similar to those registered in pre-

Conclusiones
La evaluación de la calidad del agua del río Cauca a lo largo del tramo en estudio muestra su deterioro a medida que avanza en su recorrido, identificándose tres sectores, el primero con condiciones propias de aguas de buena calidad, el segundo con un aumento en los niveles de patógenos y material particulado debido a la presencia de descargas de origen doméstico y agropecuario, y el último con valores característicos de aguas superficiales con mayor deterioro en su calidad asociados principalmente al incremento en las actividades agrícolas, industriales y urbanas en este sector y al manejo inadecuado de las fuentes tributarias, que además de problemas de contaminación por actividades antrópicas presentan procesos erosivos.
La significativa incidencia de los microorganismos patógenos y del material particulado sobre el valor final de los ICA resalta la necesidad inmediata de aplicar estrategias eficientes de manejo de vertimientos de origen doméstico y pecuario y de control de la erosión en las subcuencas, con el fin de mejorar la calidad del agua de esta fuente tan importante para el país y principalmente para la región del suroccidente colombiano.
In English ted by Álvarez et al., (2006) when assessing water quality by WQI-NSF in the Amajac river basin in Mexico.

Conclusion
Assessment of water quality along the studied section of the Cauca River showed progressive deterioration so that three sectors were identified; the first had good quality river water, the second had an increase in pathogens and particulate material due to the presence of domestic and agricultural water discharge and the third had surface water characteristics with increased deterioration in quailty, mainly due to domestic, industrial and agricultural activity in the sector and inappropriate tributary source management which, besides producing contamination problems due to anthropic activities, presented erosion.
The assessed WQI confirmed growing Cauca River water quality deterioration with increasing socio-economic activity in its basin.
The river presented overall regular to bad quality so that it must be treated for human consumption and even the incorporation of specific treatment operations such as activated carbon adsorption.
The section presenting the lowest figures for the indexes lies between Hormiguero and Puerto Mallarino water uptakes.
The high impact of pathogen microorganisms and particulate material on final WQI figures pointed out the immediate need to apply efficient strategies for domestic and agricultural discharge management and controlling sub-basin erosion to improve water quality in this important water source for the country and mainly for south-western Colombia.
Due to the high variability and complexity of Cauca River quality and its necessary use as a water source for supplying a vast number of populations besides the city of Cali, an index must be developped or adapted including representative parameters for the presence of substances causing sanitary risks in this source, such as phenols, true colour and pesticides.This index should have a similar structure to the DWQI which considers variations in time and space of the parameters comprising it and comparing these with current legislation, so that more integral river assessment can be carried out.

Figure 1 .
Figure 1.Location of sampling points on the Cauca River Wi: peso o porcentaje asignado al iésimo parámetro Ii: subíndice de i-ésimo parámetro El cálculo de los ICA se llevó a cabo mediante las siguientes etapas:

Table 1 .
Parameters measured and the analysis techniques used

Table 4
presents the average values for the physicochemical and microbiological characteristics in the river and the defined limits, according to current Colombian legislation (Decree 1594 -Minis-* Valores límite establecidos en RAS (2000) para aguas que requieren tratamiento convencional más tratamientos específicos.

Table 4 .
Physical-chemical and microbiological characteristics measured in the Cauca River in the Salvajina-Puerto Mallarino water uptake section

Distance (Km) No treatment is required for HC Unacceptable for consumption Risky Consumption Require necessarily treatment for HC Requires minor treatment for H.C. Before Suárez Hormiguero La Balsa Pass Before South Canal Before Uptake
, tal como lo reportanÁlvarez et al. (2006)en la evaluación de la calidad del agua mediante el ICA-NSF en la cuenca del río Amajac, en México. fecales