It depends upon the size of the system and the needs of your family and the way you use the solar water heater. In western countries the average annual cost for water heating is usually over half the annual gas bill. Typically a person there uses between 100L-200L of hot water a day, which can cost about $5.00 to $25.00 per person every month. A family of four could be spending between $384 to $1200 a year for hot water and heating. A gas bill is charged at varying rates or tiers, and the most costly level or tier is levied in winter, when you are using the most gas. A solar system can reduce your daily gas consumption!