EFFECT OF STORAGE CONTAINER AND TIME ON POTABLE WATER QUALITY

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Department of Engineering

ABSTRACT
Water tanks are liquid storage containers that store water for human consumption. They are usually made of polyethylene (plastic), steel, clay, ceramics and fiber glass. The need to investigate thechanges in water quality during storage in different types of water storage tanks or vessels is very crucial in establishing which tank contributes to deterioration or improvement of stored water during storage. Two sources of potable water (tap water and borehole water) were stored in twelve water storage reservoirs (six for each water source) for a period of six weeks. The tanks include black plastic tank, blue plastic tank, green plastic tank, coated steel metal tank, uncoated steel metal tank and clay pot. The water quality parameters examined were Temperature, Taste, Odour, Colour, Turbidity, Total solids, Conductivity, pH, Nitrate, Dissolved oxygen, Alkalinity, Total hardness, Calcium hardness, Chloride, Chlorine residual, Manganese, Iron, Total Heterotrophic Bacteria (THB) and Chlorophyll-A.However, all parameters listed above were analyzed at a sampling frequency of seven days interval.The results showedthat among the different container materials/colours used, black plastic tank was the best in terms ofpreserving water quality.The range in the following examined toxic parameters (i.e Nitrate, Manganese, Total heterotrophic bacteria and Chlorophyll-A) in tap water stored in black plastic tank were 8.0mg/L – 13.8mg/L, 0.099mg/L – 0.201mg/L, 2×102CFU/100mL – 116×102CFU/100mL and 0.000µg/L – 0.959µg/L respectively.On the other hand, the range for the said parameters for borehole water stored in black plastic tank are respectively 8.9mg/L – 13.6mg/L, 0.127mg/L – 0.226mg/L, 6×102CFU/100mL - 112×102CFU/100mL and 0.000µg/L –0.954µg/L. Also,findings from the study recommends that,the maximum retention period for storing tap water or borehole water in plastic tanks as well as coated steel metal tanks to be at most 3weeks while storage in clay pots should not to exceed 6days. On the other hand, uncoated steel metal tank wassuggested not to be used as storage vessel for potable/drinking water regardless of the retention time. The research also modeled the water quality results and identified that Electrical Conductivity (EC)is strongly influenced by Alkalinity, Calcium hardness and Chloride ions with R2values of 0.9926, 0.9958 and 0.9995 respectively. From this work, it was established that,black plastic materials should be considered first when selecting a container material for storing water in large capacity.