Germany′s energy saving rules come into force

> is there some other option

People in sunny climates put solar water heaters (heat exchangers) in to heat the pool.

> how does the government get me to stop heating it

Fines. If that doesn’t work, maybe they restrict gas to your home like California is starting to restrict water for places that continue to water the lawn.

Pools can be heated with heat pumps. Much cheaper than gas, even in the US. Curious if electricity is defined as resistive heat or an all out ban on using electricity (including heat pumps).

Tangentially, you can use a heat pump to move heat from within a structure into an adjacent or relatively close pool with a heat exchanger and properly configured coolant loops/condensing unit(s).

https://www.energy.gov/energysaver/heat-pump-swimming-pool-h...

> but I'm just curious how one could heat the pool without gas neither electricity.

Just be green like the government and use coal or wood to heat your pool. /s They say forests are regenerable but they only achieved renewable tree monocultures.

Coal and wood are possible. Maybe off-the-grid solar is still allowed.