kindly advise

every two days im filling water into coolant tank, and i look every where around the engine for leak but there is nothing, engine temp is normal idlling is perfect, No Over heating, But the engine oil color look like milky in the morning befor i start the engine. my question is If the water mix in to the oil why every time i check the oil level it's on mark, and where the water go and the engine runing smoth? Is it Cylender head gasket?
My Car Is Ssang yong Actyon 2008 Gasolin 4x2 Pls. Advise.