Common Sources of Dampness:

Rising Damp
Rising dampness is moisture that is soaking up a wall or floor from below the ground if an effective dpc is present rising damp should never be a problem. Traditionally built houses are perfectly able to deal with rising damp because they usually incorporate considerable ventilation opportunities such as suspended ventilated ground floors, allowing the walls to breath where they emerge from the ground. damp problems arise because the dpc has failed,not been installed correctly, or houses that were built with a traditional dpc have been modified, modifications can result in external ground levels being raised, causing increased penetrating dampness due to bridging of the dpc.

Penetrating Damp
sometimes referred to as lateral penetration, penetrating dampness refers to any moisture sourced from outside the habitable space.

This includes;
rain,snow, sleet, hail and fog, moisture from external plumbing leaks, soil, waste,rainwater.

Any moisture entering a wall above the ground,but below the dpc level [i.e. a dpc controls moisture sourced from below the ground and moisture sourced just above the ground is- penetrating damp.
Penetrating dampness also occurs through roofs,chimneys, parapet walls.

Internal plumbing leaks
Plumbing can range from tiny drips that continue for years and cause little damage, to the dramatic mains leaks that cause large volumes of water to destroy ceilings, ruin carpets and flood basements or sub floor areas. They may cause large damp patches in wall, floor or ceiling finishes, or create pools of standing water.

Below ground moisture, underground plumbing leaks, leaking ponds high water table.