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How much does a litre of hot water really cost?

You also may have wondered just exactly how much you are paying for your shower or your bath. In addition to the actual cost of the water, the total cost of a litre of hot water depends on the kind of energy used (gas, electricity or solar) and on the kind of appliance you use.

As such, for every litre of hot water, you need to factor in:

  • the price of a litre of water;
  • the write-off of the purchase price and the installation cost of your domestic  hot water generating system;
  • your energy consumption to heat this litre of water.

Cost of 1 litre of hot water according to appliance type 

The five most widely used appliances are:

The table below gives you an idea of the total cost of hot water for each appliance:

Type Cost per shower Cost shower/year Cost per bath Cost bath/year
Dual purpose gas-fired heater 0.317 € 462 € 0.767 € 1119 €
Instantaneous gas-fired water heater 0.356 € 519 € 0.806 € 1176 €
Solar boiler 0.520 € 759 € 0.790 € 1153 €
Electric boiler 0.690 € 1007 € 1.030 € 1503 €
Thermodynamic boiler 0.550 € 803 € 1.060 € 1547 €

Our calculations are based on the following parameters:

  • price of the energy sources per kWh: €0.22 (electricity) and €0.06 (gas);
  • price of a litre of water: €3.52/m3 (based on the Vivaqua rates in Brussels);
  • water consumption: 40 l (shower) and 100 l (bath);
  • the price of the dual purpose boiler does not factor in the extra price you pay compared to a regular boiler, which does not generate domestic hot water.

Choosing the right hot water system

Gas hot water system

  • The cheapest solution is the dual purpose boiler which heats both your domestic water and the water for your central heating.
  • The gas-fired water heater is also economical, but do not forget that it has a very limited hot water flow rate.

Electricity hot water system

  • The solar water heater is the most economical in terms of electrical power consumption, although it requires a higher initial investment. Moreover, if the sun is not out, you will need to heat your water drawing on another energy source (we have factored in a back-up electric boiler for 20% of the time).
  • At a lower initial outlay, the thermodynamic boiler delivers a heat output that is almost just as rewarding.

Lastly, the energy bonuses granted by Bruxelles Environnement may turn this hit parade on its head, making the solutions that are most expensive to start out with rewarding over time. 

Please note that these calculations only look at the cost element, not the ecological cost. The solar solutions are obviously most beneficial to the environment.


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