Capillarity is a property of liquids allows them to reach a certain height when inside tubes or small diameter ducts (pores). At the end, and thinking about what matters to us, it is a problem of some complexity which in turn creates other health problems and durability (bulges in the paint, plaster detachments and even structural damage) in the construction elements.
The moisture present on the ground (or on a flooded area) rises by capillary walls and partitions to a certain height, as happens in a sponge. The height will depend on several factors (porosity of the material, evaporation and moisture itself). So it is very common to find walls with moisture in the first 60 or 70 cm. These walls are literally soaked in water until that point ... and of course, also the elements that may be in the area (such as cables, pipes or pillars). Outside we see are usually dark spots and perimeter fences whitish (salt crystallization).
In general, increased capillary moisture in the rainy months (there is a greater presence of water and less evaporation) and increase your height if the wall does not sweat (eg, after applying a waterproof coating to try to remove them).
