Prefilter Housings are needed for most filters. You can choose single, double or triple. Many people use prefilters, especially if you use an under-sink model water ionizer. But even with counter-top models, prefiltering is a common practice. You can save the life of your water ionizer filters by adding prefilters. Also, for health reasons, many people like to customize their water-ionizer experience by adding specialized prefilters. Adding prefilters can reduce the amount of fluoride, chloramine, lead, bacteria, and water hardness by as much as 99%. Housings do not include the 1/4 inch hosing, as it is assumed that you already have sufficient hosing with your water ionizer. Hosing is available in the plumbing section of hardware stores.