Ground water is the main source for domestic, agriculture and industries used in Ziway-rnShala Lake area .The study area is found in the main rift valley, in rift floor which includernthe four main lakes Ziway, Langano, Shala and Abijata. The climate condition of the arearnis characterized by alternating wet and dry seasons. In the area there water qualityrnproblems. The main objective the study is to investigate hydrogeochemistry of the Ziway-rnShala Lake area system using water chemistry (chemical composition).rnThe water samples for analysis of major anions and cations are 56 water samples ofrnboreholes, hand dugs, springs, Lake Waters and River waters. Of which 31 water samplesrnare newly analyzed and the rest are secondary data from water work design andrnsupervision enterprise and zonal office of water and energy in the study area. Prior tornusing the water chemistry results for the intended application, charge balance evaluationrnis done and those with an error greater than 10 were not used.rnThe water types of most ground water in the area is Na- HCO3 specially found in Ziwayrnarea but a few samples shows water types of Na- Ca- HCO3 in Meki area and Na-rnHCO3- Cl in Shala and Abijata area which is similar water type with the Lakes whichrnindicates surface water â€“ ground water interaction. The Na-HCO3 and Na-HCO3-Clrnwater types are common in the study area.rnThe major drinking water quality problems in the area are TDS and fluorides in whichrnthe values exceed the WHO standards. This water quality problem is high towards Shalarnwhich have high fluoride, chlorides and TDS value which follow ground water flow. Thernwater type in the area is fresh, Brackish and saline based on TDS classification. In thernarea there is water quality problem for irrigation purpose. In terms of SAR the surfacernwaters (Rivers) are highly preferable for irrigation than ground water .The surface waterrnquality shows variation seasonally. They have high TDS and major ions concentration inrndry season than wet season. The agricultural activities in the area are not alarming onrnwater quality problems but the floriculture activities have some impact on Lake Ziway,rneven if the change in chemistry of the lake at present due to floriculture is not significant.rnKey words: water quality, ground water, Surface water, hydrogeochemistry, rift floor