Fouling is defined as the build up of insoluble matter on system components. This includes corrosion products, mineral scales, and microbiological matter. Cooling water systems are often susceptible to nonreactive fouling caused by settling, rather than chemical reactions. This type of fouling is especially prone to clogging because it develops in loose, porous packs that can become mobilized. Often times loose pack deposits can be flushed, but if silt or clay are incorporated into the sludge it becomes more stubborn and less likely to be flushed. 

Fouling can be controlled either mechanically or chemically. When treating fouling chemically we use antifoulants. Antifoulants can be divided in to two categories called dispersants and flocculants:

• Dispersants are synthetic polymers that are used to target and disperse insoluble matter. They also include a sub-genre called biodispersants that are used specifically to penetrate and loosen microbiological slime. 
• Flocculants are synthetic polymers with a higher molecular mass than dispersants. This higher molecular mass causes the insoluble particles to bind together rather than disperse. At which point the "flocs" can be separated from the water.