Water needs are divided into domestic and non-domestic needs, where household water consumption is one of the biggest contributors to the water crisis in urban areas. High water consumption in residential areas is due to population growth, so an awareness is needed to protect water resources. One of the efforts to maintain water resources in an area is to prepare predictions of future water needs. The method used is a dynamic system. The results show that the domestic sector still dominates water use in the Serang area even though the population growth rate is starting to slow down. Water use in the domestic sector reached 30,314,023,800 liters in 2020. The non-domestic sector experienced an increase in water demand, but the rate was still predictable, especially in terms of livestock and agriculture. The use of water in the non-domestic sector in 2020 reached 726,572,026 liters. The number of domestic needs is still high even though the number of population growth has decreased, while from a non-domestic side the increase in the number of livestock in the Serang area is still within reasonable limits because in general the growth in the number of livestock is controlled by the relevant agencies. Domestic water demand in Serang City in 2020 is 30,314,023,800 liters per year or 83,052,120 liters per day. The planning for the construction of a dual reservoir with reference to the criteria of the Directorate General of Cipta Karya is 15% -25% of the daily requirement. From this information, the reservoir volume that can be made is around 12,347,818 liters – 20,763,030 liters.