Introduction

Due to the increase of population worldwide, water demand has increased by the need to produce more food (^{Mazari-Hiriart et al., 2008}). In Mexico, much of the water is used in agriculture (^{Comisión Nacional del Agua, 2014a}), however, the demand for fresh water is higher than its availability for agriculture, reason why treated and untreated wastewater (^{Huibers & Van Lier, 2005}; ^{Mazari-Hiriart et al., 2008}) is used.

As mentioned in the study by ^{Mazari-Hiriart et al. (2008)}, Mexico is one of the main countries that uses treated wastewater for irrigation, and yet most of the time, there is no control of water quality. Given the origin of this type of water, there are standards that establish physical, chemical and biological indicators such as fecal coliforms, helminth eggs, Biochemical Oxygen Demand at five days (BOD5), Chemical Oxygen Demand (DQO) and Total Suspended Solids (TSS), pH and temperature (^{Conagua, 2014a}, ^2014b; NOM-001-Semarnat-1996) that establish their respective maximum permissible limit to maintain the quality required according to use and destiny (^{Conagua, 2013}). Studies about quality water have been conducted in different Irrigation Districts of the Mexican Republic. For example, Ahumada et al. reported a large number of fecal coliform bacteria, of the genus Enterobacter, Escherichia and Kluyvera in a 3.6 km section of La Michoacana channel in Navolato, Sinaloa. This was attributed to the fact that the channel receives irrigation runoff, discharges of domestic drainage, wastewater and solid waste (^{Ahumada-Santos et al., 2014}).

Similar studies in the DR 035, La Antigua Veracruz, DR 009 Valle de Juárez, Chihuahua and DR 049, Río Verde, San Luis Potosi reported that the amounts of fecal coliforms are above those indicated by NOM-001-Semarnat-1996 (^{Megchún-García et al., 2015}; ^{Olivas-Enriquez et al., 2011}; ^{Sarabia-Meléndez, Cisneros-Almazán, Aceves-de-Alba, Durán-García, & Castro-Larragoitia, 2011}) and even in a study conducted in the Mezquital Valley within the DR 003 and DR 100, the presence of clinically important parasites such as Ascaris lumbricoides, Giardia lamblia and Entamoeba histolytica was reported ( ^{Cifuentes, Blumenthal, Ruíz-Palacios, Bennett, & Peasey, 1994; Hernández-Acosta, Quiñones-Aguilar, Cristóbal-Acevedo, & Rubiños-Panta, 2014}).

Regarding the physicochemical variables in the DR 030, pH levels, temperature, total dissolved solids, electrical conductivity, salinity, among others were examined and it was determined that the water of that site is not recommended for agricultural use (^{Bonilla, Ayala-Osorio, González-Contreras, Santamaría-Juárez, & Silva-Gómez, 2016}).

In a study by ^{Saldaña-Fabela, Díaz-Pardo and Gutiérrez-Hernández (2011)} the physicochemical quality of water was analyzed in three points of the DR 023, San Juan del Río. In this study it was concluded that the water of this region is not suitable for use in agricultural irrigation, as well as in the conservation of biota and fish farming, besides considering the system as eutrophic.

The physicochemical and bacteriological information of water in the DR 023 is scarce, however the region is classified in environmental risk since it has a high degree of pollution (^{Saldaña-Fabela, Díaz-Pardo, & Gutiérrez-Hernández, 2011}; ^{Vázquez-Sánchez & Pineda-López, 2010}), reason why it requires an update. The aim of this study was to present an analysis of the water quality in the DR 023 in April 2015, in order to ascertain the current state of the region's water resources, as well as to warn of a possible contamination risk in water bodies, the DR 023 water is expected to be contaminated mainly by the different discharges of wastewater that receives, due to the lack of monitoring to regulate these sources of pollution.

Materials and methods

Sample collection

According to the availability of water during April 2015, samples of 53 points were taken in the District of Irrigation 023, San Juan del Río (figure 1). The water samples were collected in 100 ml plastic bottles, previously labeled. They were covered with aluminum foil and deposited in ice buckets for later analysis in the laboratory. Physico-chemical values of pH, electrical conductivity (EC), total dissolved solids (TDS) and temperature (T) were obtained with the HI9813 -5 portable Multiparameter Meter in the same area where the water samples were taken (table 2).

Figure 1 Location map of the sampling points in the Irrigation District 023 San Juan del Río Querétaro. Points 41-45 do not appear on the map because of scale matters; however, points 44-45 are the sources of supply for the dam San Ildefonso (point 43). 

Results

b) Count of Fecal Coliforms at the sampling points

Of the 53 analyzed points of the DR 023 samples of six discharges of water were obtained (figure 2), of which, when counting the CFU of fecal coliforms, it was observed that all samples, except the Kimberly discharge, exceeded the limit maximum indicated by NOM-001-Semarnat-1996 (figure 2). The points with the highest amount of fecal coliforms in the discharges were the municipal discharge San Pedro 1 with 41x10⁶ CFU in 100 ml of water. The Ponderosa discharge was the one that presented the least amount of fecal coliforms with 1.73x10⁶ CFU in 100 ml.

Figure 2 Recount of CFU of fecal coliforms in water of discharges of the Irrigation District 023. The black line represents the maximum permissible limit of fecal coliforms (2000 in each 100 ml as MPN equivalent to CFU) established by the standard NOM-001-Semarnat-1996. The graph is represented in logarithmic scale. ^{a, b, c} Equal letters indicate that the samples are statistically equal (P < 0.05). 

The water quality of dams is governed under the limits indicated by the Federal Law of Rights and Disposition Applicable on Matter of National Waters 2015. Five dams were sampled in the Irrigation District 023 (figure 3) and in all cases, the amounts of fecal coliforms are above the maximum permissible limit; the 1917 Constitution dam is the point with the lowest amount of fecal coliforms, although it is just within the maximum permissible limit (1 000 CFU/ 100 ml). The point with the highest amount of fecal coliforms corresponds to the dam La Llave with 1.73x10⁶ CFU/100 ml (figure 3).

Figure 3 Recount of CFU of fecal coliforms in dam water of the Irrigation District 023. The black line represents the maximum permissible number of fecal coliforms (1 000/100 ml as MPN equivalent to CFU) established by the Federal Law of Rights and Disposition Applicable on Matters of National Waters 2015. The graph is in logarithmic scale. ^{a, b, c, d} Equal letters indicate that the samples are statistically the same (P < 0.05). 

Of the four points corresponding to dikes, two exceeded the maximum permissible limit of fecal coliforms. The maximum number of fecal coliforms for dikes was 3x10³ CFU/100 ml, while the points corresponding to the Desander Constitution 1857 and Radial Dike 9 did not present growth of fecal coliforms.

Three points of the two Intake Works in the DR 023 (table 1) were sampled, of these; the intake work of the dam La Venta exceeded the limit indicated by the Federal Law of Rights and Disposition Applicable on Matter of National Waters 2015, with 3.3x10³ CFU in 100 ml of water.

Two sub-laterals were sampled (table 1) and both exceeded the corresponding limit of fecal coliforms, being the sublateral 9+500 the point with the highest number of fecal coliforms with 30.6x10³ CFU/100 ml. Within the DR 023, the three sampled lateral channels showed fecal coliform growth above the permissible limit (table 1). The lateral channel with the largest amount of fecal coliforms is the lateral channel 2+607, while the lateral channel Kimberly is located right at the maximum limit of fecal coliforms (1 000 CFU/100 ml).

A sample of two distinct points of the San Juan River (figure 4) was taken, and in both points the maximum permissible limit of fecal coliform bacteria according to the standard 5.66x106 CFU/100 ml. was exceeded. The San Juan River left arm had much less fecal coliforms but still exceeded the limit with 3.33 x 103 CFU/100 ml.

Figure 4 Recount of CFU in water of different points of the San Juan River of the Irrigation District 023. The black line represents the maximum permissible number of fecal coliforms (1 000/100 ml as MPN equivalent to CFU) established by the Federal Law of Rights and Disposition Applicable on Matters of National Waters 2015. ^{a, b} Equal letters indicate that the samples are statistically the same (P < 0.05). 

Also, nine drains of the DR 023 were sampled (table 1). Because of its origin, this type of water is not governed by any standard indicating fecal coliform limitation, however, almost all of them, with the exception of the Caracol drainage Tank, presented high amounts of fecal coliforms, whereas the point where more fecal coliforms was obtained was the drain Culebra with 22.66x10⁶ CFU/100 ml.

On the other hand, the water of laterals (table 1) had contrasting results with respect to the count results of the CFU, since only water from the lateral 8+100 final did not present fecal coliforms (table 1), while all the remaining laterals presented a large number of CFU exceeding the limit set by the Federal Law of Rights and Disposition Applicable on Matter of National Waters 2015, being the lateral 8+705 bridge, the point with more coliforms with 21.66x10⁶ CFU per each 100 ml. Three main channels were sampled in the Irrigation District 023 (10), on these, two points; the channel called pumps "La Valla" and discharge channel Kimberly, exceeded the limit set by the Federal Law of Applicable Rights and Disposition on Matters of National Waters 2015, with 1.33x10⁶ and 4x10³ CFU/100 ml respectively. In the case of the other main channel, the gaging station Lomo de Toro did not present a growth of fecal coliform bacteria.

Discussion

Due to the arid conditions of Mexico, the use of any economical and effective source of water has been blocked to promote the mass development of agricultural products (^{Pescod, 1992}). However, certain physicochemical variables such as pH, electrical conductivity, total dissolved solids and temperature must be considered and evaluated to guarantee the use of different water sources, since they influence the survival of microorganisms in the water (^{Ayers & Westcost, 1994}; ^{Medema et al., 2013}). According to ^{Pescod (1992)} and ^{Ayers and Westcost (1994)}, the ideal interval of irrigation water relative to pH ranges from 6.5 to 8.4; according to this, the water in most of the sampled sites is ideal for growing vegetables, with the exception of seven points, which correspond to the sublateral 2+407 road to Chintepec, La Venta dam, lateral 8+705 bridge, lateral channel 13+103 (final), well 38, lateral 8+100 crossing on the road to Chintepec, Vessel of the San Ildelfonso dam and the left arm San Juan River. Points like the Intake Work of the dam Constitution 1917, dam Constitution 1857, Intake Work of the dam La Venta, lateral channel 2+607 after well 27 are close to reaching and exceeding the established level. In Mexico, the Federal Law of Rights and Disposition Applicable on Matter of National Waters 2015 indicates a maximum value of 9 units, so under this limit the water of the dam La Venta and the sublateral 2+407 road to Chintepec, are not viable for crop irrigation. In the case of water of discharges which are subject to another pH limit value, no site exceeded the limits set by NOM-001-Semarnat-1996.

Total dissolved solids (TDS) is a variable that indicates the value of inorganic and organic compounds in water bodies (^{Fipps, 2003}), many of which are used by microorganisms to proliferate and develop. In general, the Federal Law of Rights and Disposition Applicable on National Waters 2015 indicate a value for TDS of 500 ppm in water destined for agricultural irrigation. Based on this, in the DR 023 there are 13 sites, among which stands out San Juan River, left arm San Juan River, downstream the discharge San Pedro 1, municipal discharge San Pedro 1 and before the discharges, discharge of the treatment plant San Pedro 2, discharge Ponderosa, channel of the so-called pumps La Valla. ^{Fipps (2003)} classified the possible use of irrigation water based on the amount of TDS and according to this classification, the waters of the 13 points listed above are classified as permissible (525-1,400 ppm), doubtful (1,400-2,100) and inadequate (≥ 2,100) to be used in irrigation. ^{Ayers & Westcost (1994)} also considers values similar to ^{Fipps (2003)} but with a different classification, since in this case it indicates values of water restriction to be used in irrigation; according to this, it is severely restricted the use of water of the left arm San Juan River, downstream of the discharge San Pedro 1, municipal discharge San Pedro 1, before discharges and the San Juan River because they exceed 2000 mg/l. TDS high values at these points may be due to the addition of contaminants, which means to discard the use of this water for irrigation of vegetables. Although such classifications rule out the use of certain water sources for agricultural irrigation, this can be flexible in case of considering osmotolerant crops as indicated by ^{Fipps (2003)}. Similarly, EC-CCA-001/89 indicates this flexibility in the use of water with total dissolved solids levels above 500 mg/l.

Electrical conductivity is another measure used as an indicator, along with others parameters such as total dissolved solids or sodium adsorption from water salinity (^{Olías, Cerón, & Fernández, 2015; Sarabia-Meléndez et al., 2011}), as the high salt content in the water reduces agricultural productivity by affecting sensitive crops such as beans, strawberries, among others; besides deteriorating the quality of the soil (^{González-Barrios, Calderón-Villegas, Villa-Castorena, Inzunza-Ibarra, & Catalán-Valencia, 2014}). According to the results generated in this study, the measurement of the electrical conductivity in the municipal discharge San Pedro 1 was the highest with 7580 μS/cm, compared to the other 52 sampling points. According to the proposal of ^{Olías, Cerón and Fernández (2015)} on the classification of the United States Laboratory Salinity (USLS) that define four classes of salinization risk, the samples: Municipal Discharge San Pedro 1, Vaso of the dam San Ildefonso, left arm of San Juan river and the point before the discharges are in the very high category for the risk of salinity. In this category, the measurements that are higher than 3 000 μS/cm are grouped (^{Olías et al., 2005}). Fipps classifies the irrigation water as excellent, good, permissible, doubtful and inadequate according to the measurement obtained of electrical conductivity in μS/cm. In the same way, the points mentioned above are classified as water for inadequate irrigation, since they exceed the 3 000 μS/cm, reason why the water of these points is not suitable for irrigation by its high levels of salinity. While the points corresponding to the discharge of the treatment plant San Pedro 2, downstream the discharge San Pedro 1, discharge Ponderosa and the San Juan river according to the classification of Fipps, these points are classified as doubtful water as they have of 2 000 to 3 000 μS/cm and in the modified USLS classification, these points have a high salinity risk when having from 1 500 to 3 000 μS/cm.

As mentioned in the results, the minimum and maximum temperature in water bodies were 15 °C and 30 °C respectively; the variability of the temperatures obtained in the sites could be due to the time when the sample was taken, since it is known that the water temperature is correlated with the time of day and month (^{Zheng, 2017}). However, these authors report that this is not relevant in the survival capacity and the proliferation rates of fecal coliform microorganisms (^{Lessard & Sieburth, 1983}; ^{Rozen & Belkin, 2001}; ^{Cabral, 2010}), for example, in the study of ^{Davies, C. & Evison L. (1991)} no differences were found in the survival rate of Salmonella Montevideo at 5 °C, 15 °C and 25 °C.

The data obtained regarding the fecal coliform load were compared with the limits stipulated by the Federal Law of Rights and Disposition Applicable on Matter of National Waters 2015 and NOM-001-Semarnat-1996, although the established limits are indicated with the Most Probable Number (MPN) unit, several studies indicate the equivalence between MPN and CFUs used in this study (^{California Regional Water Quality Control Board-San Francisco Bay Region, n.d.}; ^{Kougioulis, 2014}; ^{Office of Water Quality, 2006}). According to the results, 41 of the 53 points from which we obtained a water sample showed a high degree of biological contamination concerning the fecal coliform load, which was higher than the reference standards used in this study.

Municipal wastewater is the main cause that affect the quality of water bodies and soils, because most of the time they are discharged without being treated, or the proper treatment is not done (^{Cervantes-Zepeda, Cruz-Colín, Aguilar-Corona, Castilla-Hernández, & Meraz-Rodríguez, 2011}), as is the case of the samples obtained from the different dischargers of the DR 023 as they are treated water samples that do not meet the requirements established by NOM-001-Semarnat-1996 (figure 2). The only sample that complied with the standard was the Kimberly discharge, which did not present fecal coliforms. These results show that these waters represent a potential health risk, because contaminated water and its poor treatment increases the risk of acquiring diseases such as: diarrhea, cholera, dysentery, hepatitis A, poliomyelitis among many others (^{“OMS | Water,” n.d.}). That is why it becomes essential that the wastewater receives the appropriate treatment that guarantees the minimum quality requirements, to prevent pollution of rivers and dams. Contrary to what ^{Cisneros-Estrada and Castanedo-Guerra (2014)} mention, the treatment plants San Pedro I and San Pedro II, do not comply with the maximum permissible limits allowed by NOM-001-Semarnat-1996, about the number of CFU of fecal coliforms, so the use of these waters for agricultural use is not recommended.

Most of dams exceed the maximum permissible limit, except for the dam Constitution 1917 (figure 4), this is worrisome because it is not known what the source of contamination of these dams is, so it is probable that clandestine discharges are causing such contamination. In the case of the dam San Ildelfonso, the sample corresponding to the Vessel/glass/vase, has very high CFU levels (figure 4), however, the samples that correspond to the intake work, do not present CFU (table 1). This may be due to the fact that fecal coliforms are found on the surface and not in deep areas, because they do not stand a long time in the water and require very specific conditions for their survival (^{Madigan et al., 2004}) and the water that is released into the intake work is from the deep part of the dam San Ildefonso. The samples that correspond to the San Juan River present very high levels of contamination, this agrees with previous reports (^{De la Llata-Gómez, Rivera Sánchez, Valtierra, Martínez Reséndiz, & Montoya Martínez, 2006}) so there is evidence of biological contamination in the San Juan River and in addition, there are reports not only of biological contamination, but also of chemical, reason why the use of this water represents a risk for the inhabitants of the zone (^{de la Llata-Gómez et al., 2006}).

It is likely that in the entire network of distribution of the DR 023, there is contamination caused by clandestine discharges from nearby houses in the area or nearby establishments such as greenhouses or factories, as there is a variation in contamination levels by CFU of fecal coliforms, as can be seen in the samples corresponding to dikes, sub-laterals, laterals and main channels. For example, the lateral 8+100 had high levels of coliforms and in the sample belonging to the final part of the same, there was no coliform presence, so it is suggested there is only one source of contamination near the beginning of the lateral, however, when sampling was done, this source was not detected. Drain samples were taken for comparison of the levels of water contamination, which should in theory be treated and of untreated water as the case of drains (table 1), however in the Damper Tank Caracol drain, the presence of CFU of fecal coliforms was not found, this may be due to the place where the sample was taken.

Conclusion

The physicochemical and bacteriological data of the DR 023 water provides information on the water quality. It is recommended A constant monitoring of the parameters presented, including the coliform load is recommended to guarantee the use of certain water sources to irrigate crops in the region, as well as a more strict supervision of the operations of wastewater treatment plants, due to the high fecal coliform load present in the water of these DR 023 plants. Poor water quality is due to the presence of pollution sources by clandestine discharges as: surrounding houses, greenhouses and factories. As well as the inadequate treatment of water coming from the treatment plants of the area that alter the quality of the water for irrigation. This fact warns us about the risk to the health of the population who uses these waters. Also, recommendations can be given to avoid planting crops such as vegetables that can be infected by this type of water and are potentially harmful to the population.