Как сообщать об изменениях расчетного привязанного свойства класса в WPF?

Подскажите, пожалуйста, где я не прав.
Я создал класс Bill, в котором есть ряд полей.
Есть форма, на которой расположены TextBlock'и в них попадают значения полей класса Bill через Binding
Вопрос в следующем - как мне просуммировать значения TextBlock и вывести сумму в поле Total?
Вот класс Bill

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace BindWork.Models
{
    public class Bill : INotifyPropertyChanged
    {
        private int hotwater;
        private int coldwater;
        private int electric;
        private int hotwatertax;
        private int coldwatertax;
        private int electrictax;
        private int total;
        public int HotWaterTax
        {
            get { return hotwatertax; }
            set
            {
                hotwatertax = value;
            }
        }
        public int ColdWaterTax
        {
            get { return coldwatertax; }
            set
            {
                coldwatertax = value;
            }
        }
        public int ElectricTax
        {
            get { return electrictax; }
            set
            {
                electrictax = value;
            }
        }

        public int HotWater
        {
            get { return hotwater; }
            set
            {
                hotwater = value;
                total += hotwater;
                OnPropertyChanged("HotWater");
            }
        }
        public int ColdWater
        {
            get { return coldwater; }
            set
            {
                coldwater = value;
                OnPropertyChanged("ColdWater");
            }
        }
        public int Electric
        {
            get { return electric; }
            set
            {
                electric = value;
                OnPropertyChanged("Electric");
            }
        }
        public int Total
        {
            get
            {
                return total = coldwater + hotwater + electric ;
            }
            set
            {
                OnPropertyChanged("ColdWater");
                OnPropertyChanged("HotWater");
                OnPropertyChanged("Electric");
            }
        }
        public event PropertyChangedEventHandler PropertyChanged;
        private void OnPropertyChanged(String info)
        {
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(info));
            }
        }
    }
}

А вот форма

<Window
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:BindWork"
        xmlns:Models="clr-namespace:BindWork.Models" x:Class="BindWork.MainWindow"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Window.Resources>
        <Style TargetType="{x:Type TextBox}">
            <Setter Property="FontSize" Value="36"/>
        </Style>
        <Style TargetType="{x:Type TextBlock}">
            <Setter Property="FontSize" Value="36"/>
        </Style>
    </Window.Resources>
    <Grid>
        <Grid.DataContext>
            <Models:Bill/>
        </Grid.DataContext>

        <TextBox Text="{Binding Path=ColdWater, UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Height="57" Margin="10,10,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="231" Cursor=""/>
        <TextBox Text="{Binding Path=HotWater, UpdateSourceTrigger=PropertyChanged}"  HorizontalAlignment="Left" Height="57" Margin="10,70,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="231" />
        <TextBox Text="{Binding Path=Electric, UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Height="57" Margin="10,132,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="231" />
        <TextBlock x:Name="ColdWaterBill" Text="{Binding Path=ColdWater, UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Margin="435,10,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Height="57" Width="347" />
        <TextBox x:Name="ColdWaterTax" Text="{Binding Path=ColdWaterTax}" HorizontalAlignment="Left" Height="57" Margin="247,10,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="184" IsReadOnly="True" />
        <TextBox x:Name="HotWaterTax" DataContext="{Binding Source=Bill}" Text="{Binding Path=Electric}" HorizontalAlignment="Left" Height="57" Margin="246,70,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="184" IsReadOnly="True" />
        <TextBox x:Name="ElectricTax" HorizontalAlignment="Left" Height="57" Margin="246,132,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="184" IsReadOnly="True"/>
        <TextBlock x:Name="ElectricBill" Text="{Binding Path=Electric, UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Margin="435,132,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Height="57" Width="347" />
        <TextBlock x:Name="HotWaterBill"  Text="{Binding Path=HotWater, UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Margin="435,70,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Height="57" Width="347" />
        <TextBlock x:Name="TotalBill" Text="{Binding Path=Total, UpdateSourceTrigger=PropertyChanged, Mode=OneWay}" HorizontalAlignment="Left" Margin="435,194,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Height="57" Width="347" />
    </Grid>
</Window>

Где я ошибся?