What are the disadvantages of using activated charcoal filters in water treatment?

The enormous inner surface of the activated charcoal and the plentiful supply of nutrients for microorganisms increase the risk of microbial contamination and the formation of biofilm. The remedy is a hot-sanitisable activated carbon filter. However as a rule, activated charcoal filters should only be used when considered absolutely necessary.

[GMP Compliance Adviser, Chapter 5.B]