Cold and Granular Activated Carbon filtered Water Dispensers (CGWDs) have been marketed as the solution for those who have access to drinking water of proper quality but wish to have immediately available cold water with a better taste than drinking water. CGWDs are devices that are i) directly connected to the drinking water network, ii) equipped with a Granular Activated Carbon (GAC) filter, and iii) equipped with a cooling reservoir. CGWDs are widely used and are becoming even more popular. However, in previous studies, CGWDs appeared to be vulnerable to bacterial growth, i.e. the bacterial quantities in the effluent had increased compared to those in the influent. More alarming, however, was the presence of opportunistic and pathogenic bacteria in the effluent, while being absent in the influent. The objectives of this study are to assess whether suggested measures can decrease the bacterial growth within CGWDs and to examine whether the free chlorine and organic matter removal performances are affected by the implementation of these measures.
The degree of bacterial growth in CGWDs could be decreased with the implementation of the boiler with an integrated GAC filter. By exposing the CGWD to steam prior to the experiment the degree of bacterial growth in the CGWD could be reduced even more. Placing the GAC filter into the boiler prevented the bacteria from growing onto the filter material. On the other hand, it was not enough to keep the heterotrophic bacteria from growing to numbers above the applicable standard. However, with the application of steam, it was possible to reduce the numbers of HPC22 below the detection limit during the first 37 hours. This shows a potential for periodic steam sterilization of CGWDs. Moreover, placing the GAC filter into the boiler increased the TOC removal efficiency of the CGWDs. Implementing a boiler as pretreatment ensured that the effluent of the CGWDs contained no free chlorine.