Water is important for concrete, a billion liters of fresh water are yearly used for mixing and curing. But at the moment, fresh water is scarce in the world. The saltwater is or will be very convenient and economical in the construction; especially in the coastal area. Therefore, the use of saltwater causes side effects such as corrosion in the steel on RC. So, this thesis focused on the effect of saltwater on concrete and the prevention of rust in steel-reinforced concrete. The main aim of this thesis is the experimental investigation of the effect of saltwater using a compression strength test and also using paint coating methods to prevent rust on reinforcement concrete by flexural strength test. the concrete cubes were 100 mm on each side and beams were 100mm x 100mm x 500mm, the mix ratio was 1:1.5:3 for M20, the concrete specimens were cured age are 7 and 28, 60 days. The compressive strength result on the 7 th day is the using saltwater for mixed and cured (SS) are 1.2%, 3.5%, and 8.2% more strength than using freshwater for mixed and cured (FF), saltwater mixed and freshwater for curing (SF), and freshwater for mixing and saltwater for curing (FS) respectively. While, the FF at 28 days are 3.5%, 19.5%, and 22.9%, and at 60 days are 8%, 9.7%, and 13% higher strength than a using SS, SF, FS respectively. In flexural strength results, the used paint coating reinforcements are 18.7%, 14.5%, and 6.7% more flexural strength than without coating reinforcement on the 7 th , 28 th , and 60 th day respectively. Keywords: Saltwater, Freshwater, Compressive Strength, Flexural Strength, Steel Corrosion, Rust Prevention, and Paint Coating Method.