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Water Softeners Can Cause Problems


The NAHB Research Center has learned that installing an undersized water softener in a residential plumbing system can reduce the flow of water to some of the fixtures in the home. Undersizing can also reduce the water softener’s efficiency, causing it to deliver "hard" water.

The Research Center has also learned that, in certain circumstances, installation of a water softener in a home with a residential fire sprinkler system can potentially cause safety problems by reducing flow and pressure below the sprinkler system's requirements.

The NAHB Research Center has published a guide to help builders and plumbers avoid these problems when installing water softeners.

Water Softener Flow Capacity

The pressure and flow rate of water in home plumbing systems are reduced when the water passes through water softeners. Softeners are manufactured in a range of flow capacities to accommodate the requirements of different homes. Their size must conform to plumbing code requirements and must accommodate the house's water needs.

Utilizing provisions of the U.S. model plumbing codes (UPC, SBCCI, CABO, and IPC), the Research Center's guide helps builders and plumbers to determine the proper flow capacity for water softeners on the basis of the number and type of plumbing fixtures in the house.

Many water softeners have rated flow capacities of five to eight gallons per minute. Plumbing code requirements and actual water demand for many homes can be considerably greater. In addition, requirements for anticipated water demand are different in various local plumbing codes.

For example, the Uniform Plumbing Code (UPC) requires that a house with two-and-a-half baths must have a water flow capacity of seventeen gallons per minute, while the CABO Plumbing Code requires that a similar size house must have a flow capacity of eight gallons per minute. In order to comply with code requirements, it is imperative to determine which plumbing code is used in the city or county where the home is located.

Fire Sprinkler Systems

Safety issues can be raised by incorrect installation of water softeners in homes with fire sprinkler systems. When possible, water softeners should be installed downstream of the take-off for the fire sprinkler system, to avoid impact on the sprinkler system's flow and pressure needs.

If water softeners are installed upstream of a sprinkler system, they can reduce downstream flow and pressure below the system's requirements.

Pressure requirements for home sprinkler systems, which are specified in National Fire Protection Association Standard 13D, are a flow of twenty-six gallons per minute plus pressure of about twelve psi. Pressure loss for water passing through water softeners can be about fifteen psi. A pressure of at least twelve psi must remain after water has passed through the water softener.

In combined systems in which the sprinkler system piping supplies cold water to domestic fixtures, the water softener cannot be isolated from the sprinkler system and will reduce the flow and pressure to the system. The size and flow of the water softener must account for these factors.

Labeling and Certification

Prior to purchasing a water softener, builders and plumbers should check the device's flow rate and pressure drop. These should appear on a label affixed near the softener's water connection, or in the manufacturer's literature.

The manufacturer should also state that the water softener has been tested by a third-party certification agency for compliance with the requirements of Water Quality Association Standard 100.

Purchasers can take the following additional steps:

  • Ask the water softener contractor for technical literature on the product;
  • Ask the water softener contractor to document compliance with the local plumbing code;
  • Check with the local plumbing code enforcement agency for their requirements;
  • Check with the Water Quality Association, 630-505-0160, for product certification status;
  • Review Plumbing Code Requirements and Sizing Guide for Residential Water SoftenersPDF file - Adobe Acrobat Required.