The topic of my bachelor’s thesis is absorption of light in water and connection with attenuation. The theoretical part of the thesis comprises physical processes due to which the water molecule turns into different excited states. These are electronic, vibrational and rotational states. The excited electronic states are the reason for absorption in UV and visible part of electromagnetic spectrum. In relation to this, the thesis also includes a concept of molecule orbitals. The concept is essential for understanding of electronic levels in a molecule. The empirical part of the thesis is based on the measurement of light attenuation at wavelengths λ=633 nm and λ=405 nm, and also in the UVA part of the sunlight spectrum in dependence of water depth. The coefficient of absorption was determind by fittiing the curve to measured data and compared with values in literature. Finally, the theses stated at the beginning of my bachelor’s thesis are assessed.