**6. Water quality indices of surface and underground water sources in Nigeria**

This section provides the water quality indices of surface and underground water sources from different part of Nigeria. Several authors have applied water quality index (WQI) to evaluate the quality of water from different water sources especially surface and underground water across the different zones in the country [18, 47, 49–51]. Herein, the country is divided into four regions (south, east, west and north) and the WQI of water from different sources including rivers, boreholes, hand-dung wells etc. of the country is discussed.

Several researchers have assessed and reported the WQI of water bodies in the Southern states of the country [47, 52–55]. Most of the rivers investigated in Bayelsa: Korama, Otamiri, Oramiukwu, Ase, and Orashi Rivers showed poor water quality, and water environment clearly unsuitable for drinking [46]. The Otamiri and Orimiukwu Rivers have very bad water quality based on the WQI while the Ase River was observed to have bad water quality with a high degree of deterioration at the downstream [52]. The Orashi River displayed a marginal level of pollution as about 50% of parameters failed to meet the required standards [54]. The Brass River in Bayelsa State was considered to be far from excellent [53].

Aigberua and Tarawou [56] investigated the WQI of some surface waters (rivers) in the Rivers State along the Taylor Creek area of the state. Their calculated water quality indices (WQIs) scores fall within the range which indicates water quality status tending from "poor water quality" to "unsuitable for drinking". Taylor Creek shows a slightly acidic water environment that contains high levels of nitrate loading, pH, total dissolved solids and *E. coli* in addition to an objectionable level of color and unsightly appearance. The WQI assessment reflects water of poor quality and generally unsuitable for public consumption. The presence of multiple dumpsites mostly from leachates along the stretch of the river may be responsible for the poor degradation in water quality. It was therefore recommended that the water is not fit for human consumption or and recreational purposes. Overall, the WQI assessment of Taylor Creek revealed that water is unsuitable for drinking and may pose serious health risks.

The water quality index (WQI) approach was used to assess the suitability of water from three local government areas in River state by Chinwendu [57]. The result of these assessments indicated that borehole water was unsafe for human and animal consumption. These waters had an acidic pH while the dissolved oxygen, temperature and calcium values were not within the WHO and NSDWQ permissible drinking water standards. The water quality index of the borehole waters in the region exceeded permissible water quality standards in all sampling locations due to groundwater contamination resulting in water that was unsafe for human and animal consumption.

The suitability of water from different sources (stream, borehole and pipe - born water) were assessed using the WQI in the Niger Delta region of Nigeria by Etim et al. [58]. The concentrations of the respective parameters are below the WHO/ ICMR standards. The quality of water based on the index number representing overall suitability of the water indicated that the water samples analyzed from pipe born and borehole water were safe for human consumption and domestic purposes while the samples analyzed from stream water are not safe for human consumption.

The quality of some river bodies around the Warri metropolis was evaluated by Godwin and Oborakpororo [59] based on their various physico-chemical parameters. The results obtained from the study showed that all the surface water samples were found to be unfit for human consumption with very high turbidity and suspended solids. The presence of fecal coliform in the various water bodies was much higher than the stated standard of regulatory agencies. The physicochemical parameters of groundwater in 12 cluster boreholes in Enugu North district/region, southeast Nigeria categorized all the water samples within the range of good to excellent [60].

The quality of 12 different water sources and 2 treated water used by peri-urban town in the West region of Nigeria were evaluated to assess their suitability for drinking and domestic us [61]. Water quality parameters included pH, temperature, acidity, total alkalinity, chloride content and coliform. The results indicated that all the physicochemical parameters of the water samples complied with regulatory standards. Similarly, most sites complied with heavy metals criteria. At these sites, fecal coliform and *E. coli* tested positive for all the samples except one tap water sample. The majority of the water samples (86%) were rated as excellent based on the physicochemical parameters. However, the inclusion of microbiological data in the WQI revealed that only 7% of the samples analyzed can be regarded as excellent water. Akoteyan and his team [62] studied the water quality characteristics of Owo river for municipal water supply in Lagos-Nigeria. The study showed that the physical parameters assessed (electrical conductivity, pH, total hardness, anions and cations) were within the maximum permissible limit of WHO standard for drinking water quality. The calculated WQI showed that the water is suitable for *Application of Water Quality Index for the Assessment of Water from Different Sources… DOI: http://dx.doi.org/10.5772/intechopen.98696*

human use. Olagbemide [63] applied the WQI for the assessment of Eleyele Lake, Ibadan, to check the quality of the lake water with respect to different physicochemical parameters using standard methods. Water samples were collected from different river sites (i.e., before the lake, on the lake and after the lake). The results of the Water Quality Index showed that the water quality at these sites was poor. This suggests that the lake is polluted and not totally safe for human consumption without proper treatment. Very high values were obtained for color, turbidity, total solid, total suspended solid, BOD, COD, alkalinity, phosphate, chloride, magnesium, nitrate, total organic carbon, total organic matter were observed and all were above the permissible WHO values.

Murtala and Ahaneku [64], studied some physicochemical parameters (pH, dissolved oxygen, temperature, turbidity, total dissolved solid, nitrate, ammonia, iron, lead and chromium) from the river Asa in Illorin (Kwara state) and presented the complex water quality data of the river as the WQI that can easily be understood by the technical and non-technical personnel. The result of the Water Quality Index showed that three of the four stations investigated should be ranked as poor and the remaining station as marginal. The implication is that the river failed the Drinking Water Quality Index and is not suited as a potable source of drinking water. The seasonal variation of some physicochemical properties of River Asa in Kwara state was also assessed and the river water quality status was evaluated using CCME Water Quality Index. The result of the study revealed the river is not suitable source for drinking water.

Ogbozige and co-workers [65] assessed 12 water quality parameters (turbidity, TDS, pH, Cl�, EC, DO, BOD5, COD, total nitrogen, total phosphorus, Fe and Mn) for the River Kaduna, Nigeria on a monthly basis for a period of one year at 15 sampling locations using standard methods. The data were used to develop Water Quality Index (WQI) across the 15 sampling locations. The WQI revealed that the water quality of four (4) sampling locations was poor and the general water quality of the remaining 11 sampling locations was marginal. The water quality assessment of water consumed in Kaduna State revealed that among the 15 rivers, 4 of the rivers (Kutimbi, Kigo, Breweries and Rigasa) recorded poor WQI while the river upstream of Narayi community was marginal. Results indicated that the quality of the rivers at Narayi and Rigasa communities was bad. The water qualities of the remaining 8 rivers were of better quality including River Romi. Based on the results, the WQI of River Kaduna on the Canadian scale is mostly marginal. Yisa [37] evaluated the quality of selected hand-dug wells in Maikunkele area in Niger state using WQI technique. These results indicated that the quality of the samples was marginal while one location was extremely bad. The results also revealed a high contamination of coliform in the samples and nitrate concentration above standard of WHO, EPA, APHA and the Nigeria drinking water standards.

The Water Quality Index and heavy metal contents of underground water sources in Doma Local Government Area, Nasarawa State, Nigeria was investigated to ascertain the suitability of the water for domestic purpose using physicochemical parameters: temperature, turbidity, TDS, TSS, pH, EC, total hardness, alkalinity, chloride, nitrate and sulphates in the water samples [66]. The physicochemical parameters determined for borehole and hand dug well water samples (i.e., temperature, turbidity, total dissolved solids, total suspended solids, electrical conductivity, total hardness, alkalinity, chloride, nitrate, and sulphate) were all within the standards recommended by regulatory bodies NSDWQ and WHO. The mean pH for the hand dug well water was within the recommended standard values; however, the pH value for the borehole was outside the range recommended standards (the water was slightly acidic). The WQI evaluated for both borehole and hand dug well water samples showed the ground water sources presented good water quality. The results of the mean metal concentrations in borehole and hand dug well water samples shows that the concentrations of Cd, Cu, Pb and Zn are within the permissible limit recommended by regulatory bodies while those of Cr and Fe are higher than standard values. Oko and his crew [67] collected water samples from boreholes and hand dug wells located in two wards in Wukari town in Taraba state and assessed some physico-chemical parameters using analytical methods. The calculated WQI showed that the water samples from the borehole was of better quality for drinking than the hand dug well.
