Regarding the OpenWeatherMap water level being very dynamic, I am looking into that now. Hopefully will have a solution soon (which should be a server change).
The OWM key is managed and paid for by us (OpenSprinkler). This is to avoid users having to register with a new site and retrieve a key for personal use. Instead we believe the cost will be reasonable for us to manage and maintain it. This will also allow us to be more responsive as API’s change, etc.