###### Contents  
* 1 Introduction
* The contamination of water resources, including marine, lake, river, and drinking water, by pathogenic bacteria, such as _E. coli_, enterococci, and _Salmonella_ spp., is one of the major current problems with a profound social and economic impact in the world [1]. The limited number of sanitation and water disinfection infrastructures means that over a billion people worldwide lack access to clean drinking water [1; 2; 3]. Drinking water, if contaminated with microorganisms, can lead to waterborne diseases such as giardiasis, cholera, gastroenteritis, and associated symptoms such as vomiting, abdominal cramps, and headache [4; 5]. A lack of safe drinking water is estimated to cause around two million deaths each year, most of them children under the age of five [6]. To prevent the onset of waterborne diseases, there are effective water disinfection procedures, such as chlorination and ozonation [7; 8]. However, these processes paradoxically lead to the formation of toxic disinfection byproducts, such as trihalomethanes and other carcinogens, which are harmful to human health and the environment [7; 8]. In recent years, alternative technologies for water disinfection have been studied [9; 10], also based on nanotechnologies. Antimicrobial nanomaterials such as silver nanoparticles (AgNPs) have attracted increasing attention for water purification. However, in addition to the data, albeit limited, on the possible danger of the absorption and nanotoxicity of NPs for both humans and the environment, the application of AgNPs for water purification is very expensive [11] and has been associated with mammalian cell cytotoxicity [12; 13]. Very recently, antibacterial cellulose (cotton) nanocomposite fabrics (CNCFs) with in situ generated AgNPs using medicinal plant _Vitex_ leaf extract have been prepared using a simple, low-cost, and environmentally friendly method [14]. In our opinion, although the scope of this study was to develop antibacterial cotton fabrics for medical applications, the materials produced by the authors could also have potential for application in water decontamination. Recently, an attractive and environmentally friendly approach consisting of converting crayfish shells and their derivatives to functional materials for environmental applications, such as adsorption and/or antibacterial materials for waste-water purification, has been reported [15]. In this study, it was also demonstrated that the attachment of Ag-TiO\({}_{2}\) nanoparticles to the crayfish-shell biochar carriers optimized their antibacterial ability and facilitated recycling [15]. The addition of effective antibacterial agents to infected waters could be an option to reduce bacterial contamination, but the difficult removal of residual antibiotics limits the application of this strategy. To overcome this problem and avoid post-treatment procedures, a smart solution could consist of immobilizing the antibacterial agents or inserting antibacterial compounds on insoluble polymeric matrices (resins) that act as a support [16]. With the birth of solid-phase organic synthesis (SPOS), various resins have been synthesized and employed in daily life for their many advantages, including excellent mechanical strength, high chemical stability, good weather resistance, and ease of further functionalization [17; 18; 19]. During studies to develop an alternative method of disinfection with insoluble polymeric materials, it was found that cross-linked poly-(vinyl-pyridinium halide) (PVPA) had a new and remarkable ability to remove bacteria from water. In this case, mechanistic studies revealed that PVPA was capable of irreversibly capturing bacteria during treatment [20]. Subsequently, ion-exchange resins have been used to retain microorganisms by direct treatment of cell suspensions [21; 22; 23; 24]. Differently from the case previously reported, this time, the adsorption of microorganisms on the resins was reversible and the microorganisms were obtainable by desorption from the resins.