Another couple of considerations, FWIW....
If you only plan to fully-empty the pool every 10 years or so, you may find the water pretty soupy towards the end!!! You'll be adding chemicals (especially chlorine, presumably) to keep the water clear, plus algicides, etc. If you don't change a fairly high proportion of the water pretty often, the chemical load will be nasty to swim in. I can't remember the numbers but public pools change water at the rate of x litres per swimmer visiting, all the time.
If you DO find that you need to dump several thousand liters of water per year into the main sewer, have a look at your water bill. There's a bit for water supply and a bit for drainage. The latter is calculated on the basis of charging 100 percent of the volume that comes INTO the property. If you can LEGALLY dump the pool water somewhere else and PROVE that it is NOT going to the sewer, you can get the charges reduced.
If you only plan to fully-empty the pool every 10 years or so, you may find the water pretty soupy towards the end!!! You'll be adding chemicals (especially chlorine, presumably) to keep the water clear, plus algicides, etc. If you don't change a fairly high proportion of the water pretty often, the chemical load will be nasty to swim in. I can't remember the numbers but public pools change water at the rate of x litres per swimmer visiting, all the time.
If you DO find that you need to dump several thousand liters of water per year into the main sewer, have a look at your water bill. There's a bit for water supply and a bit for drainage. The latter is calculated on the basis of charging 100 percent of the volume that comes INTO the property. If you can LEGALLY dump the pool water somewhere else and PROVE that it is NOT going to the sewer, you can get the charges reduced.