I tested two of the five sensors. The sensor return values which are always a multiple of 16, so when doing my measurements I divided the values by 16 to make them easier to compare (e.g., comparing 1090 to 1141 vs comparing 17440 to 18256). The rest of my comment uses the divided values.
When dry the sensors return a value between 0 and 8. Once it gets wet the values jumps up to about 120 so it's easy to detect the presence of water.
The story is very different when trying to measure depth. I put the sensor into a small vial, added water, and used a ruler to determine the sensor was immersed to about 17mm, then started taking readings. The initial value was 850 but was fluctuating with a bias towards a slow increase. I figured it was going to take some time (maybe a couple minutes) to settle down. After a couple minutes I recorded a low of 840 but noticed it was still increasing. After 20 minutes it had gone up to 1000 and was still increasing. (As I write this it's up as high as 1023 and is still increasing with a bias towards increasing.) So as a depth sensor it has too much variance to be useful. Consequently I will use this as a flood alarm (e..g., if a sump pump fails or the washing machine drain overflows).
You do want to ensure that the electrical connections (above the copper sensor grid) don't get wet. You can try to waterproof it but a better (and easier) way is to mount the sensor in something like a pill container. Turn the pill container upside down so the opening is at the bottom, and drill a small hole at the height of the middle of the sensor grid. The hole serves two purposes, (a) to give you a place to run your wires, and (b) to allow water to enter the chamber. Water will only enter up to the level of the hole, as the air above the hole will prevent water from going any higher, thus keeping the electronics dry.
Finally, if using this as a depth sensor, remember that copper will oxidize, and the resulting chemical compound is poisonous, so don't use this sensor to touch any water you (or your pet) will consume.