People can make soft water harder by adding a water hardener to their water, but some caution is advised when using a water hardener, depending on how the water is being used. As a general rule, soft water is better for pipes and appliances, so people who have problems with laundry and showering because their water is too soft may want to think about some alternatives before using a water hardener. In the case of aquarists, who use water hardeners to reach the right chemical balance in their fish tanks, it is a very good idea to consult a guidebook which discusses all of the issues involved with water hardeners before making soft water harder.
Soft water is simply water which lacks a number of dissolved minerals, most notably magnesium and calcium. The lack of dissolved minerals means that soft water is less likely to form stains and calcifications on pipes and appliances, and it also reacts differently with soaps and detergents. For example, soap tends to froth more freely in soft water, which can create a soapy residue on people or garments after washing.
When people want to make soft water harder because of problems with soap, they have a couple of options. They can attach a water hardening unit to their water system, making all of the water in the house harder with the use of chemicals, or they can address the problems caused by extremely soft water where they emerge. With laundry, for example, a small amount of baking soda can be thrown in with each load to harden the water, with the side benefit of deodorizing the laundry, and less laundry soap should be used with each load. People may also want to check their laundry detergent for water softeners, as many firms add softeners in case people are laundering in hard water.
In the shower, using soap products which are as pure as possible can help reduce the feeling of slickness or slime after showering in soft water, and people should also more generally use less soap because of the increased lathering. It is also possible to find water hardener units which attach to showerheads, making soft water harder as needed.
Aquarists can add commercial water hardeners to their aquariums, but they should only do so if they are comfortable with chemistry. Testing kits can be used to determine whether aquarium water is hard or soft, and the results of these tests can be used to select the best chemicals to make the soft water harder. Things like magnesium sulfate and calcium chloride are often sold along with commercially formulated hardeners for aquarists who want to be able to tweak the water hardness even further.
