Factors such as population increase and industrialization, coupled with the establishment of touristic villages, have necessitated an upgradation of water treatment plants (WTPs) in Egypt. In this study, three different water source alternatives were designed and compared with a simple decision matrix to select the most appropriate one for upgrading and extending the Mariout 2 WTP. The first two alternatives are located on the k-40 Alex-Cairo desert road and k-77 EL Nasr canal, respectively, where the water source is obtained from the Nile River. The third alternative is located at the k-51 Alex-Matrouh coastal road and a non-conventional seawater source is used. The design results showed that the required energy power of the first, second, and third alternatives were 0.31, 0.066, and 0.72 kw/purified m3, respectively. The operational costs of the first, second, and third alternatives were 0.665, 0.426, and 6.621 EGP/m3, respectively. The cost of the intake pipes was found to be the lowest for the third alternative, whereas it was found to be the highest for the first one. Based on the results obtained from the decision matrix, the third alternative was found to be the most appropriate alternative followed by the second one. This study may assist in making decisions regarding the water source selection and treatment methods for the extension of the fourth stage of the Mariout 2 WTP.