Required modifications for water level control
To make the fill control for the water tank you should be able to use the same microcontroller as the one shown in the example. In that case an Atmel AVR was used.

The circuit would require the addition of an output from the AVR that would go to a buffer circuit that would in turn be used to turn an electronically controlled water valve on and off.

Then the software if the AVR would have to be modified to control the fill valve ON/OFF state based upon the level sensor states. The simplest scheme would simply turn the valve ON when the level 9 was not active and then when the water filled enough so that once the level 9 changed state the valve would be turned to the OFF state. An alternative would be to select some other lower level to use for detecting of the valve ON state and then turn OFF when level 9 showed the tank was once again full.

The fill valve usage assumes that there is a pressurized source of water from which the water is supplied to the tank. On the other hand if a pump was required to move water from say a pond into the tank then the pump ON/OFF could be controlled in place of the fill valve.