The circuit drawn above, is used to indicate when water reaches a certain level in a container or to indicate the moisture level of soil for plants. For a water indicator, one contact goes on the inside bottom of the container and the other contact is placed on a certain level of the container, where the light would light up when the water reaches that level. The led can be replaced with a buzzer to alarm that the water reached the level, or replace the led with a relay which could turn on a pump or other appliances to drain the water.
For the soil detector, place one contact in the soil and the other contact in the soil as well, but place it at least half a feet from the other contact. When the led is dim, it means you need to wet the soil, as you make the soil moist, the led glows brighter. You can stop watering until the led is brightly lit.
On the left picture, shows the circuit that i made, where it has 2 copper contacts that can be placed in the soil.
Detector contact placement for soil and water are below in diagram:
