Introduction:
Groundwater is the basic resource of water for drinking and domestic purposes.  Several areas, worldwide depend  on groundwater  , especially those   have  shortage in surface water supply  and   mostly inadequate for drinking purposes , '[Zhou et al., 2020; Subba Rao et al., 2020]. Ground water may be subjects to deferent types of contamination; this contamination is spread and consider  impact  issue on both national and international  scales [Gao et al., 2020; He et al., 2020].  There are many activities such as , erratic rainfall, the rapid growth of urbanization, intensive irrigation activity, excessive usage of fertilizers and unplanned industrialization, population growth, man-made/anthropogenic and geogenic pollution often lead to a large amount of groundwater contamination [Gao et al., 2020; Kumar et al., 2020; Subba Rao et al., 2020; Wu et al., 2019]. Monitoring  process of groundwater sources is important due to  it gives  valuable information on characteristics of water safety and  regular change in water quality, water quality categories,   and treatment options for polluted water [Suk and Lee 1999; Kaown et al. 2012]. As a consequence of, intake of polluted drinking water is occurrence several health problems in varied locations and areas around the world [Adimalla and Qian, 2019b;Wu et al., 2020; Yadav et al., 2019]. A number of studies have reported the importance of using various methods not only to quantify the groundwater quality but also to evaluate the pollution sources and vulnerable distribution [Badeenezhad et al., 2019; Egbueri, 2020; Subba Rao and Chaudhary, 2019]. Turbidity in water is caused by deferent suspended particles like clay, silt, finely organic and inorganic matter, soluble colored organic compounds, plankton and other microscopic organisms.  If  the turbidity of water is more than 5 NTU we need to  some kind of treatment to remove turbidity  because is necessary before water subjects  to disinfection by chlorine, due to its effects, both on the acceptability of water to consumers and the selection of efficiency of treatment processes, particularly the efficiency of disinfection with chlorine [WHO, 1997].  High levels of turbidity in drinking water can create nutritional value and  provide habitat for pathogens.  So if not removed excessive turbidity can promote regrowth of pathogens in the water source and  leading to waterborne disease outbreaks, that may be caused significant cases of intestinal illnesses worldwide.  Increase levels of turbidity measurements in drinking water can demonstrate a numerous things such as a decrease in source water quality, improper water treatment or defect in the water supply system [CDW, 2012].  High levels of turbidity in groundwater does not proven pathogen presence only but gives information on general water quality and also it consider  as an indicator of surface influence on groundwater quality [Martin,Allen, et al.,2008]. All water sources that intent to use for drinking purpose should be monitoring and make control process for turbidity in the distribution supply including at the consumer’s points. For effective operation of the drinking water supply, turbidity levels should be approximately 1.0 NTU or less entering the distribution system [CDW, 2012].  Turbidity can be used as an indicator for conditions that permit potential microbiological growth in the water supply system [EPA, 2006].

2. Water quality index:
(WQI) Quality of water can be classified into differ  scales  that indicate the status of water quality with the help of WQI. The conceptual of WQI was first used by Horton [1965],  as following scales Water quality rating Grading 0–25 Excellent, water quality 26–50 Good, water quality 51–75 Poor, water quality 76–100 Very poor, water quality >100 Unsuitable water quality (Bharti and Katyal 2011; Gibrilla et al. 2011; Lumb et al. 2011a, 2011b; Sahu et al. 2011; Sen 2011; Maruthi Devi, et al.2011;Srivastava et al. 2012; Dede et al. 2013). The main aim of WQI is to convert the complex water quality data into understandable and usable information by which major people can know the status of water sources in a particular region [Vasanthavigar et al. 2010; Akoteyon et al. 2011; Islam, s. et al. 2011; Balan et al. 2012]. The weighted arithmetic index method was used for the calculation of WQI   using the following: Eq. [1] (Brown et al. 1970).

WQI = Wi Qi / Wi [1] The unit weight (Wi) for each water sample is calculated by the following formula: Wi = K/Si,[2]
Where K is appropriately constant and Si is the standard permissible value of the i the parameter. The quality rating (Qi) of Eq. [1] is then calculated as under: Qi = 100 [(Vi − Vo/Si − Vo)], [3] 

Where Vi is estimated concentration of i the parameter in the analyzed water and Vo is the ideal value of this parameter in pure water. All ideal values are taken as zero for drinking water except pH = 7.0 [Laskar and Gupta 2011; Tyagi et al. 2013].

2.2 study area:
Shendi Town  it is the third largest Town in River Nile State, it located about 176 km north of Khartoum  [ capital of republic of Sudan ] ‚ and 130 km south of El damer ( capital of River Nile State).  It is in the arid zone of Sudan with annual rain fall ranging between 0 and 119mm per year.( Suleiman ,2011). Shendi town has no sewerage system and it has a distribution system of drinking water; the whole Town depends on ground water as source of drinking.                             

2.3 Study population: water sources, water supply system and household facilities.

2.4 sample size determination: Sample size was determined according to WHO guidelines, therefore 150 samples were examined based on total of population in study area.

2.5 Water sample collection:
Water samples were collected according to the WHO Guidelines for drinking water quality assessment (WHO, 1993). Water samples were collected from all  ground water sources, distribution system and storage facilities ,   Samples were stored in 500-ml plastic bottles (high-density polyethylene bottles recycled from similar, bottled distilled water products), cleaned with liquid detergent, and rinsed with distilled water and air dried.  A “control wash” was employed by prerinsing the collection bottle 3 times with 20 ml of the sample water before final collection. Bottles were filled completely to the brim to avoid inclusion of air, and bottles were capped tightly and appropriately labeled. Samples were stored overnight in the refrigerator, not cooler than 4°C, and were tested within 24 h. 

2.6 Water samples analysis:  
Turbidity was measured according to standard methods for examination of water by the following steps: Filtered a portion of the sample through a GF/B filters paper, Filled a test tube with filtered sample and retain for use as the BLANK tube, Filled a test tube with unfiltered sample to the 10 ml mark, Selected a turbidity choice on photometer and took photometer reading as NTU.

2.7 Data analysis:
Data were analyzed by computer using both Microsoft Excel and Microsoft word, and then the results are displayed in tables and other statistical graphs.