using System;

​

interface IConsume {

    double CalculateWaterConsumption();

}

​

public class Plant : IConsume {

    // Or use private fields

    double A1 { get; set; }

    double A2 { get; set; }

    double A3 { get; set; }

    public Plant(double a1, double a2, double a3) {

        A1 = a1;

        A2 = a2;

        A3 = a3;

    }

    public double CalculateWaterConsumption() {

        return A1 + A2 + A3;

    }

}

public class MainProgram

{

    public static void Main()

    {

        var plant = new Plant(10, 10, 2); // Or Plant plant = ...

        Console.WriteLine(plant.CalculateWaterConsumption());

    }

}