So it worked for most of the day, but then ran into battery problems. As the NRF needs 3.3v, the 328, is less fussy and can take 1.8v to 5.5v, while the water sensor needs 5v though ive tested it down to 4.3 ok. (not going to test it over 5v though) .

So in my initial test i had 3xAAA batteries, 2 going to the 328 and RF and the 3rd just the water sensor. But overnight as the batteries dropped down to about 1.3v each (4.2v total) the sensor stopped working. And the RF now on 2.6v also stopped.

Trying to avoid running a regulator 24/7 to save wasted power, i thought about my options, and am going to try this next.

2xAA batteries running the 328, which will work with either alkaline or nimh. The 328 drives a pnp transistor, that switches this same voltage on off as needed to make readings. Once "on", the voltage will then go to a DC-DC boost module that boosts it up to 5v for the water sensor, this is also then regulated down to 3.3v for the RF. The reading is made and sent off then the 328 turns this circuit off, and puts its self to sleep until the next reading time.