The aim of this study was to compare the 5E learning model with traditional learning methods in terms of their effect on students' conceptual understanding of water subtopics such as water hardness, water softening, water pollution and water purification. The study adopted Pretest Posttest non-equivalent quasi-experimental design. The participants of the study were 8 grade section A 54 students registered for second semester 2013 E.C academic year at dilchibo primary school in Bahirdar. While 27 of them were randomly assigned to the experimental group, the other 27 were assigned to the control group. The researcher continuously taught both groups for one month. The experimental groups were taught with 5E instructional model of the constructivist approach whereas the students in the control group were taught with the traditional approach. Both qualitative and quantitative research methods were used in this study. The data collection instruments were tests (pretest-posttest), observation, as well as informal assessment. A Chemistry Achievement Test (CAT) consisting of 20 questions were developed by the researcher to apply before and after treatment to both groups. The informal assessment also administered before and after intervention. Besides, the observation was conducted from the first day up to the last day of the intervention. Chemistry Performance Test on water concepts which also tested retention with a reliability index of 0.653 was developed, validated and used for data collection. Research questions were answered using mean and Standard deviation, while the null hypotheses were tested using t-test at 0.05 level of significance. The data obtained from pre- and post-tests of both groups was compared with the independent sample t-test and paired sample ttest. The results from pre-tests showed that there was no significant difference between control group and experimental group. On the other hand, the post-test results showed that there was a significant difference between groups in favor of the experimental group. Also, the experimental group’s perception of motivation in classroom learning environment during the treatment was higher than that of the control group. It is essential that teachers should develop their skills for designing a constructivist-learning environment within class. With this aim, teachers should be given in-service training. th