A portable water softener is a travel-sized version of residential or home water softening devices, designed to reduce the hardness of small quantities of water or act as filtration devices for local water sources. Often using an ion resin, the softening devices are able to filter excess mineral content — primarily calcium and magnesium — from water. The ion resin generally replaces the minerals with sodium ions to produce softer water; sodium is found in normal salt, which is commonly an active ingredient in the water softening process. Other terms for the portable water softener include portable descaler, portable dionizer, and portable limescale remover.
Softening water with a portable water softener reduces the possibility of accumulated mineral deposits, or "scaling," on metal surfaces frequently in contact with hard water, including pipes and faucets. It also minimizes the sticky reaction of hard water with soap. Many cleansing substances such as dishwashing liquid or powder, bath soap, and shampoo react poorly with hard water to produce a filmy residue that clings to affected surfaces.
Campers often use a portable water softener in recreational vehicles (RVs), to soften shower and dish washing water. Softening the water prevents a film from building up on dishes, and helps prevent adverse effects to skin and hair from bathing in soap mixed with hard water. While some softeners store water in their own reservoir, others pump it directly into an RV's clean water tank.
Many portable softeners require no power, and can be connected directly to a fresh water supply as a filtration device. The softeners contain quantities of solar or rock salt, which provides the sodium ions necessary for softening. The salt wells must be refilled periodically, as repeated use dissolves the salt and depletes the supply of sodium ions.
Portable water softeners are also sometimes used for car washing. Softening the water prior to washing a vehicle can prevent residual mineral buildup that could dull or even damage the finish. The type of portable water softener intended specifically for this purpose generally uses a customized design, meant to fit between a garden hose and a spray nozzle. Hard water passes from the hose and through the softening filter, then passes from the filter into the spray nozzle as soft water. More fitted and/or specialized designs for softeners include those for shower heads and kitchen sinks.
Some portable softeners offer water purification capabilities, doubling as both a softener and a filter for drinkable water. Others come with hardness monitors, which periodically test the mineral content of stored water or a water source against acceptable levels. These devices usually require batteries or an external power source.