I don't know if there is a small alternative for water detection as good as them. I tried searching but what I am getting was these sensors. So if you guys know any small size sensor to detect water presence please let me know. And if it comes with buzzer it will be a lot of help.
The sensors shown are simply conductors separated by an insulating space. When water, which conducts electricity slightly when pure (or much better with dissolved ionic substances), bridges the gap, it completes the circuit. All you need are two conductors, separated from each other by an insulator such as air, PCB plastic or cloth.
If expense is a priority, make your own. Just weave two bare copper wires in parallel through a piece of nonconductive material such as nylon fabric. You can customize the size, flexibility and other qualities to your needs. For a bed-wetting or diaper sensor, use thin wires and material for comfort, going to two heavier ones for the connection to the rest of the circuit, for strength. For a diaper alarm, just put the sensor in an are likely to get wet; there's not need to wrap the whole diaper. BTW, disposable diapers contain absorbents that prevent the outside from getting wet, and I do not suggest putting a sensor inside, against a baby's sensitive skin. Ummm... and sterilize the sensor after use with bleach or hot water.
The solid PC boards you show might be more useful in detecting water on a floor or window, though.