Discoloration: Place a drop of household bleach on a suspected mold spot; if the stain loses its color or disappears, it may be mold. 2. Musty/earthy smell: This may indicate the presence of some types of mold. 3. Water stains or dampness: These indications of a moisture problem will often lead to mold if left untreated. Learn more about how a moisture meter can help find moisture and mold growth.