The Buriganga River encompasses the south-western periphery of Dhaka City. Thirty three water samples were collected from Dhaka of which 16 during rainy season and another 11 at the time of dry season from the Buriganga river (surface water); and samples from different high-rise buildings and the rest 6 samples from different residential buildings and industries (surface water) during dry season. The dry season samples were collected from the data of March 25 to 30 and the wet season samples were from 20 to 22th August in the year of 2011. The sites of water sampling for different sources of waters were shown in Figure 1. The water sample was collected in one liter plastic bottles. These bottles were cleaned with dilute hydrochloric acid (1:1) and then washed with tap water followed by distilled water. Before sampling, containers were again rinsed 3 to 4 times with water to be sampled. In case of river water, sample was drawn from different points and few centimeters (10-15 cm) below the surface. The collected samples were sealed immediately to avoid exposure to air. The water carried to the laboratory of Bangladesh Agricultural Research Institute (BARI), Gazipur for testing. The samples were analyzed as quickly as possible on arrival at the laboratory.
Determination of water pH and EC of the water sample: The pH of water samples were determined electrometrically (Ghosh et al., 1983) using pH meters (HI 8424 Model). The EC of collected water samples was determined electrometrically using conductivity meter (Model 8423) (Tandon, 1995).
Total dissolved solids (TDS) of the water sample: Total dissolved solids (TDS) were determined by weighing the solid residue obtained by evaporating a measured aliquot of filtered water samples to dryness (Chopra and Kanwar, 1980).
Determination of sodium and potassium of the water sample: Na and K were determined with the help of a flame emission spectrophotometer (Model Jenway PEP) at 768 nm for K and 589 nm for Na (Golterman, 1971 and Ghosh et al., 1983).
Determination of carbonates, bicarbonates, chloride, and nitrate of the water sample: Carbonates and bicarbonates of water samples were determined by acidimetric method of titration (Tandon, 1995). Chloride of water samples was analyzed by argent metric method of titration (Ghosh et al., 1983 and Clesceri et al., 1989). Nitrate was determined by phenoldisulphoic method with the help of a spectrophotometer (Coleman junior Model NO. 6A) set at 420 nm wavelength (Ghosh et al., 1983).
Determination of phosphorus, sulphate, calcium, magnesium, zinc, copper, iron manganese and boron of the water sample: Phosphorus was determined colorimetrically with a spectrophotometer (Coleman junior Model No. 6A) at 660 nm wavelength (Olsen et al., 1954). Sulphate was estimated truribidimetrically with the help of spectrophotometer (Model Spectronic Genesys TM5) at 425 nm wavelength Wolf, 1982 and Tandon, 1995). Complex metric titration was used for estimating the calcium from the water samples (Page et al., 1982). Magnesium was analyzed by complex metric method of titration (Page et al., 1982). Zinc, copper, iron and manganese were analyzed by atomic absorption spectrophotometer (Hitachi, Model-170-30) at the wavelengths of 213.8 nm, 324.8 nm, 248.3 nm and 279.5 nm, respectively (Clesceri et al., 1989). Boron status of water samples was determined by using curcumin-oxalic acid with the help of a spectrophotometer (Coleman Junior Model No. 6A) at 540 nm wavelengths (Allen et al., 1974 and Ghosh et al., 1983).
Determination of sodium adsorption ratio (SAR), potassium desorption ratio (PAR), soluble sodium percentage (SSP), residual sodium carbonate (RSC) and hardness (HT) of the water sample: The following formulae related to the irrigation water classes rating were computed from the data obtained by chemical analyses of water samples following Das (1983). The equations were-
RSC= (CO3-- + HCO3--) - (Ca++ + Mg++)
HT= 2.5 x Ca+++4.1x Mg
Where, concentrations of ionic constituents for calculating all parameters except hardness in me l-1 and in case of hardness as mg l-1.
The correctness of analyses of water samples were checked following the methods described by APHA (1995). The difference between the anion and cation sums falls between acceptable limits (5-10%) and the percentage of difference is calculated on the basis of the following equation.
The TDS values were calculated from the summation of major cationic and anionic constituents (mg l-1) which are as follows:
TDS= (CO3-- + HCO3- + Na++ K+ + Ca++ + Mg++ + SO4-- + NO3-+ CI- + SiO3-)
The electrical conductivity (EC) were also calculated from the summation of cation or anion (me l-1) as follows-
Electrical conductivity (EC) = 100 Î Σ cation or anion, me l-1
The acceptable criteria for the ratio of calculated or measured TDS to EC is from 0.55 to 0.70. The criteria for acceptable ratio is as follows-