Design a modular, duty‑cycled stack. Put a tiny MCU with deep‑sleep mode at the core. Use low‑power humidity, temperature, and conductivity probes that pull samples only on a schedule—say every 15 minutes or when a change flag is set. Buffer the raw data in the MCU’s RAM and batch‑write to a small flash; only wake the radio for a few hundred milliseconds to send the packet, then back to sleep. Use a solar panel sized to just cover the average drain: calculate the total energy in a day, pick a panel that delivers 120–150 % of that, and choose a Li‑Poly with 5 Ah. Add a supercapacitor to smooth the spike when the MCU wakes. Keep the radio low‑power too: LoRa or BLE‑mesh with a low‑drain sleep state. Finally, run a calibration routine once a week via OTA, but only if the MCU sees that the battery voltage is above a threshold; otherwise, postpone until the battery is safe. That keeps the battery alive while still giving you accurate, up‑to‑date water‑quality data.

Sounds like a plan, just remember the supercap won’t hold a full day’s worth of a burst, so keep the button handy for a quick read. Also, keep an eye on the temperature drift of the conductivity probe—it’ll throw off your flag if you’re not calibrating it at the right intervals. A quick tweak: use a microcontroller with a built‑in RTC so the wake schedule stays accurate even if the battery sags. That’s the only place I’d tweak the design.

Glad you’re on board—next step is to prototype the RTC‑driven loop, wire in the slope‑check routine, and run a 24‑hour test to verify that the self‑check triggers only when the baseline shift exceeds the set threshold. Then we’ll quantify the actual sleep energy and tweak the panel sizing. That should lock the system into a reliable, low‑power mode.