Parts of the U.S. have what is commonly referred to as “hard water,” and people who live in these areas battle the problems that hard water creates. The most common defense against hard water, which is a nuisance but not a health hazard, is to install a home water softener.
Water softening involves exchanging calcium and magnesium minerals present in the water – which cause the hardness – with sodium. As the water softener processes gallon after gallon of hard water on a daily basis, the treatment capability of the softener becomes depleted and must be recharged or regenerated.
Regenerating the unit uses a large quantity of sodium-rich water, called “brine”, that must be disposed of. In homes with onsite septic systems, this brine flows into the septic tank and eventually makes its way to the system’s drainfield.
People using home water softeners often wonder whether these units might cause problems for their onsite septic systems. Some common questions consumers ask are:
- Do water softeners hurt the bacteria that work in a septic tank?
- Does the additional amount of water from water softener regeneration affect a septic system’s performance?
- Does the concentrated salt water used in regeneration decrease the drainfield’s ability to absorb wastewater?
Unfortunately, experts don’t all agree on the answers to these questions. Research has been done that resulted in acceptable conclusions to many people in the industry, but some authorities believe that more studies are needed to determine what impact, if any, brine has in a septic system.
What Makes Water Hard — And How Does It Become Soft?
As water flows through layers of rock underground, it picks up loose particles and dissolves minerals from its surroundings. Because of this characteristic, and the kind of rock common in many aquifers, calcium and magnesium minerals are frequently found in household water. Water with substantial amounts of calcium and magnesium is referred to as “hard water.”
Hard water minerals reduce water’s ability to function effectively in our homes. For instance, bath soap combines with the minerals and forms a pasty scum that accumulates on bathtubs and sinks. Homeowners must use more soap and detergent in washing, so expense for these products increases.
These minerals also combine with soap in the laundry, and the residue doesn’t rinse well from fabric, leaving clothes dull. Hard water spots appear on everything that it is washed in and around the home – from dishes and silverware to the family car. Hard water not only affects household cleaning, but the minerals also can build up on the inside of pipes in the plumbing system; and in water heaters, the minerals settle on the heating element, the walls of the tank, in the hot water pipes, and in faucets where they produce a scale (similar to the original rock) that reduces the efficiency and life of the hot water system
Water Softeners Make Water Work Better
Water softeners combat this nuisance by eliminating the minerals that cause hard water. The most common kind of water softener is a mechanical appliance plumbed directly into the home’s water supply intake. The water softener exchanges calcium and magnesium with sodium in a process called ion exchange.
The water softening system consists of a mineral tank and a brine tank. The water supply pipe is connected to the mineral tank so that water coming into the house must pass through the tank before it can be used.
The mineral tank holds small beads (also known as resin) that carry a negative electrical charge. The positively charged calcium and magnesium (called ions) are attracted to the negatively charged beads. This attraction makes the minerals stick to the beads as the hard water passes through the mineral tank.
Eventually the surfaces of the beads in the mineral tank become coated with the calcium and magnesium minerals. To clean the beads, a strong sodium (salt) solution held in the brine tank is flushed through the mineral tank. Sodium ions also have a positive electrical charge, just not quite as strong as that of calcium and magnesium. This large volume of sodium ions overpowers the calcium and magnesium ions and drives them off of the beads and into the solution. The sodium solution carrying the minerals is then drained out of the unit. Some sodium ions remain in the tank attached to the surfaces of the beads.
The Softening Process
The normal water softening cycle operates like this:
Hard water enters the mineral tank. Inside the tank, the calcium and magnesium ions carried in the water attach themselves to the beads. The surfaces of the beads eventually hold their limit of calcium and magnesium and can’t remove any more from the water. At this point the water softener must be “regenerated.” The three-step regeneration cycle can be scheduled according to a timer or by a flow detection meter.
The first step, called the backwash phase, reverses the water’s flow and flushes any accumulated dirt particles out of the tank and down the drain. Next, in the regeneration or recharge phase, the sodium-rich brine solution flows from the brine tank into and through the mineral tank. The brine washes the calcium and magnesium off the beads. In the final phase, the mineral tank is flushed of the excess brine, which now holds the calcium and magnesium, and the solution is disposed of down the drain.
Sodium ions from the previous regeneration cycle cling to the beads. Now, when the hard water flows into the mineral tank, the calcium and magnesium ions change places with the sodium ions on the resin. The displaced sodium ions remain dissolved in the water.
Home septic systems
Knowing how a septic system works helps home-owners understand why adding something like water softener regeneration brine may cause problems.
A conventional septic system consists of a septic tank, a distribution box, and a drainfield, all connected by pipes. When wastewater flows from the house, it is temporarily held in the septic tank where heavy solids (sludge) settle to the bottom. Lighter materials float on the surface of the water in the tank and are called the scum layer. This separation is known as primary treatment.
The solids that collect in the bottom of the tank and the materials that float in the scum layer are partially decomposed with the help of bacteria that occur naturally in human waste. The liquid between the solids and the scum flows out of the tank through a baffle (or a tee) and into a distribution box. The distribution box evenly separates the flow into a network of drainfield pipes. Each pipe has holes in its underside that allow the water to drain into gravel-filled trenches. The water slowly seeps into the soil beneath the trenches where it is further treated. This process is called secondary treatment.
Important Note: As sludge accumulates in the bottom of the tank and its level rises, new wastewater coming from the house has less time for suspended particles to settle into the sludge layer. These suspended particles can flow into the absorption field.
The septic tank must be pumped out periodically to remove the accumulated sludge and scum and to prevent clogging the drainfield.