Chloride levels in many surface waters are increasing and pose an emerging environmental concern, since elevated chloride levels are harmful to aquatic life in freshwater. Communities across the U.S. have observed surface waters with chloride water quality impairments, and chloride levels in groundwater are also increasing.

A major source of chloride is water softening, although depending on where you live road salt and fertilizers may be larger sources. In homes that have moderately to very hard water, many use water softeners. Water softeners remove hardness which causes scale buildup in pipes, appliances and water fixtures, and deposits on glassware. Ion-exchange water softeners use salt, usually sodium chloride, for recharging. In general, the less salt we are discharging to the environment the better, particularly if the discharge could reach fresh or groundwater. 

First question – Is a softener needed?

Hardness less than 5-7 grains per gallon (gpg) typically does not need to be softened. With publicly supplied water, the water hardness can be obtained from the water utility or city. Some cities soften the water at the drinking water plant. If data is not available the water should be tested by a professional, or a property owner can buy a kit and test it themselves.

Second question – What kind of softener?

There are two primary types of softeners — time or demand. Older/lower-cost softener regeneration cycles are time-clock initiated, using electronic timers or clocks to recharge the resin at a preset time and day. This wastes salt and water because they regenerate whether or not it’s necessary. Demand softeners use a more sophisticated method called demand-initiated regeneration where regeneration is based on the measured amount of water used. To reduce salt usage, high-efficiency softeners should be used; include one or multiple features highlighted below:

• Efficiency rating of 4,000 grains/lb salt or higher
• Upflow or countercurrent regeneration
• Hardness sensors and water meters
• Variable reserve
• Regeneration with softened water
• Twin tanks

With demand systems, if the owners are conservative in their water usage they will use less water and therefore less salt. Also, not all water needs to be softened. Certainly water used outside the home should not be softened and some properties will only soften hot water or the water for specific appliances, such as water heaters or dishwashers. If the water in the home is high in iron content, it can clog the resin in the softener. A prefilter will help cut down on salt usage. If the water supply has high chlorine due to being publicly supplied, a chlorine filter will also increase the efficiency of the softener.

The high efficiency softener should be set for the actual hardness of the water and serviced at the recommended frequency, which will also minimize salt usage and ensure the system is set appropriately and performing. There are other options on the market to reduce hardness and/or minimize scaling, but data about their performance is not yet conclusive.

Third question – Is regeneration water bad for septic systems?

The amount of brine/regeneration water is typically 30 to 80 gallons per cycle, and in some homes it may only run once or twice weekly. If the salt is kept to the minimum, the research to date is not conclusive whether problems will be caused. But as discussed, the less salt the better for the environment.

If the water softening system is not efficient or the unit is not operating properly, the amount of salt added to the system may be detrimental to microorganisms in the septic system. In these cases, the concerns include that the regeneration water may:

• Cause an increase in the amount of solid material staying suspended in the effluent of the septic tank. These solids may shorten the life of downstream components.
• Prevent the formation of scum layers (typically composed of fat, oil, grease and soaps) in septic tanks therefore causing more of these materials to travel to downstream components.
• Impact treatment in advanced treatment units such as media filters or aerobic treatment units. Many manufacturers do not allow the generation water to enter their units due to treatment concerns. 

Fourth question – Where should the recharge water go?

In cities, the brine drains to the sanitary sewer where it travels to a wastewater treatment plant. Unfortunately, it isn’t feasible for most WWTPs to remove chloride, which is dissolved in water. When the levels of chloride are high in the discharge to lakes, rivers and streams, upgrading softeners or removing hardness at the source with lime are typical solutions.

In areas served by septic systems the brine often discharges to the septic system, although this is not generally a recommended practice as large amounts of salt can be detrimental to the system. Since the regeneration water has not been contaminated by bacteria, viruses or organic material, it technically does not need treatment in the septic system. Before considering any of the options below, be sure to check with your local and state regulations to determine legal discharge options.

The brine can be directed into the collections system of footing drains. This may require the installation of a sump to collect this water. This high salt content can be hard on vegetation.

• The brine can be day-lighted to the surface if it does not directly discharge into a water body.
• The brine can go into a drywell, an old abandoned drainfield, or a small separate section of drainfield with 20-50 feet — typically sufficient (must have some separation to the water table).
• The brine may be rerouted directly to the primary soil treatment system to prevent agitation of the layers in the septic tank or the performance of an advanced treatment system. 

Final thoughts

Chloride in the softener discharge cannot be treated in a septic system and will eventually end up in surface or groundwater.

In general, the less salt discharged from water softeners the better for the environment and our septic system. We should encourage property owners to only use one when and where they need it, use and maintain an efficient demand-based unit, and route the brine out of the septic system when needed.