A simple support to fix 2 nails.
With this you can get a diy and cheap soil moisture support to supervise with an Arduino a plant, a water reservoir...

The scad file is parametric and can be adjusted for your nails and purpose.

Weld one wire to each nail.
One wire goes to an Arduino digital output (5 volts when activated).
The second wire to a resistor (10k is standard) then to ground.
Between the resistor and the ground another wire goes to an Arduino analog input.

To get a measure with the Arduino, simply activate the digital output, wait for 2-3 seconds (measure need to stabilize) and you get the moisture measure from 0 to 1024.
0 when in the air and about 750-850 when the nail are in water.

The sensor is sensible to water but also to temperature (coef is about 0.2 to 0.3) and to salt (water with salt will need a bigger resistance.

I used this diy sensor to supervise soil moisture for plants and also to check is a water reservoir is full or empty.

Warning : depending on nails and you measure frequency, nails tend to be damage by electrolyze, so it's necessary to have a low frequency for measure. For soil monitoring a measure to 10 to 15 minutes is enough.