Thank you all for quick responses!
I really love the idea behind this @Mahko_Mahko : Gas meter from Xiaomi/Aqara door sensor (ZigBee)
I did try already with one spare aqara door sensor and didn’t get it to work without any further wiring (I think my water meter magnetic field is not strong enough). I already order some reed from aliexpress to try “the external version”.
I also order a ESP32 to try the deep sleep + BLE concept from Aliexpress… 10 days… I’ll keep you posted!