The following are methods for accurately calculating the capacity of water tanks based on different actual needs:

For domestic water storage

Residential use: Consider the number of residents in the household or building and their daily water consumption habits. On average, each person may consume around 100 - 300 liters of water per day for daily activities like drinking, cooking, bathing, and flushing toilets. For example, if there are 5 people in a household, and assuming an average daily consumption of 200 liters per person, then the daily water requirement is 5 × 200 = 1000 liters. Considering factors like possible water supply interruptions or the need to store water for a certain period (e.g., 1 - 2 days), you can multiply this daily amount by the number of reserve days. So, if you want to store water for 2 days, the required water tank capacity would be 1000 × 2 = 2000 liters or 2 cubic meters.

Small public facilities like schools or offices: Estimate the number of people using the facility and their water usage patterns during working or school hours. For schools, in addition to students, you also need to consider teachers and staff. For example, a small school with 500 students and 50 teachers, assuming an average daily water consumption of 50 liters per person (considering mainly toilet flushing and some drinking water during school hours), the total daily water consumption would be (500 + 50) × 50 = 27500 liters. Again, depending on how many days of reserve water you want to have (say 1 day for emergency backup), the water tank capacity should be around 27.5 cubic meters.

For industrial water storage

Cooling water in industrial production: First, determine the heat exchange requirements of the industrial equipment. You need to know the heat load of the equipment (usually measured in kilowatts, kW), the temperature difference between the inlet and outlet of the cooling water (ΔT, in °C), and the specific heat capacity of water (which is approximately 4.2 kJ/(kg·°C)). The mass flow rate of the cooling water (m, in kg/s) can be calculated by the formula m = Q / (4.2 × ΔT), where Q is the heat load of the equipment. After getting the mass flow rate, convert it to volume flow rate (knowing that the density of water is about 1000 kg/m³). Then, considering the circulation time of the cooling water in the system (e.g., how often the water is completely replaced or replenished), you can calculate the required water tank capacity. For example, if the volume flow rate of the cooling water is 1 m³/s and the circulation time is set to be 10 minutes (i.e., 600 seconds), then the required water tank capacity is 1 × 600 = 600 m³.

Process water in manufacturing: Analyze the production process and the amount of water needed at each stage. For example, in a beverage production factory, you need to consider the water for ingredient mixing, rinsing bottles, and equipment cleaning. Calculate the maximum amount of water required during peak production hours for each process and sum them up. If the mixing process requires 5 m³ of water per hour, bottle rinsing needs 3 m³ per hour, and equipment cleaning uses 2 m³ per hour during peak production, and assuming the production process runs continuously for 8 hours a day, then the daily water requirement for the process is (5 + 3 + 2) × 8 = 80 m³. Depending on whether you need to store water for overnight or during equipment maintenance periods, you can determine an appropriate capacity for the water tank.

For fire protection water storage

Residential and commercial buildings: According to building codes and regulations, the fire water tank capacity is usually determined based on the building's height, area, and fire protection classification. For example, for a multi-story residential building with a height below 54 meters and a certain fire protection area, the minimum fire water tank capacity may be required to be 18 m³ to ensure there is sufficient water for fire extinguishing equipment like fire hoses and sprinklers to operate for a certain period during a fire emergency. In commercial buildings with a larger area and more complex fire protection systems, the required capacity may be calculated based on factors such as the number of sprinkler heads, the flow rate of the fire extinguishing system, and the required fire-fighting duration (usually ranging from 10 minutes to several hours depending on the specific situation).

Industrial plants: In industrial areas, considering the larger fire hazards due to the presence of flammable materials and complex production processes, the fire water tank capacity is calculated based on the maximum possible fire area, the type of fire extinguishing agents used (such as water spray systems, foam systems), and the fire-fighting time required. For example, in a chemical plant with a high risk of fire, if the estimated fire area requires a water flow rate of 50 liters per second for effective fire suppression and the designed fire-fighting time is 30 minutes (i.e., 1800 seconds), then the required fire water tank capacity is 50 × 1800 = 90,000 liters or 90 m³.

For agricultural irrigation water storage

Farmland irrigation: Calculate the water demand of the crops based on the cultivated area, crop type, and local climate conditions. Different crops have different water requirements per unit area. For example, rice fields may need about 5 - 10 mm of water per day per square meter during the growing season, while wheat fields may require around 2 - 5 mm per day per square meter. If you have a rice field with an area of 10,000 square meters, and assuming a daily water requirement of 8 mm per square meter, then the daily water demand is 10,000 × 0.008 = 80 m³. Considering factors like irregular rainfall and the need to ensure continuous irrigation during dry periods, you can decide on an appropriate water tank capacity for storing irrigation water, such as storing water for 3 - 5 days, so the tank capacity could be 80 × 3 to 80 × 5 cubic meters depending on the reserve days you choose.

Greenhouse irrigation: In greenhouse agriculture, the water usage is relatively more precise and depends on the types of vegetables or flowers being cultivated and the irrigation method used. For example, for a greenhouse growing tomatoes using a drip irrigation system, the water consumption may be around 2 - 3 liters per plant per day. If there are 1000 tomato plants in the greenhouse, the daily water requirement is 1000 × 2 = 2000 liters or 2 cubic meters. Similar to farmland irrigation, you can consider storing water for a certain number of days to determine the appropriate water tank capacity based on the stability of the water supply source and the irrigation needs during different growth stages of the crops.