Water is considered the artery of the life and one of the valuable gifts with which God has blessed us. Rapid population growth and development require strong management strategies to conserve water resources, especially in arid and semiarid countries. Moreover, existing water resources must be protected from pollution and used in an efficient way. Polluted waters must be treated using cost effective treatment methods. The objective of this study is to improve water quality of Hajamta Reservoir in Al Jabal Al Akhdar, Sultanate of Oman, using a custom-made treatment system, to enhance the supply of water for the Shanut village. Based on previous studies, reservoirs in Jabal Akhdar suffered from eutrophication and pollution. For example Hajamta reservoir was built in 1996 for domestic purposes, but it was eutrophic and some people were afraid even to feed their animals from this reservoir. Therefore, custom-made treatment system was designed and constructed at the reservoir in Shanut. A specific program was undertaken to evaluate the water quality of the reservoir before and after the filtration. Seventy seven samples of water were taken for a period of about two months. For each sample physical, chemical and biological parameters were analyzed. Acceptance of the treatment unit was determined through questionnaire survey. In addition, a model of the treatment system was tested in the lab under control conditions to evaluate the effect of sand depth of the filter on quality, quantity and flow rate of the effluent, The results from the treatment unit at Hajamta Reservoir showed general improvement in water quality. For example water turbidity was reduced by 87% and suspended solids were reduced by about 86%. Furthermore, total coliform bacteria were completely removed after the treatment. The effect of the system on total dissolved solids (TDS) was negligible. However, TDS values were within Omani Standards for wastewater reuse and disposal. Eventhough the value of Biochemical Oxygen Demand of untreated water was small, the reduction due to treatment was 31%, and Chemical Oxygen demand reduction due to treatment was 62%. Based on the survey results 100% of respondents agreed that treated water could be used for washing clothes and cleaning homes. The 100% of the interviewees said no algae were found and there was no bad smell in the treated water. Furthermore all the respondents agreed to store treated water in closed tank. Most of the interviewees (85%) indicated that the system was easy to operate and 95% of the participants would like to have the system in their homes. When the depth of the sand filter increased from 22 cm to 27 cm in the lab model, the production water and flow rate decreased whereas the quality of the water improved.