What Is A Water Softener?

A water softener is a fairly simple filtration system that treats hard water. This system has two primary parts: the softener tank and the brine tank. 
As water flows through the softener tank, the positively charged minerals such as calcium, magnesium, iron, and sodium attach to the negatively charged tank. The filtered water then continues through the plumbing system and is distributed throughout your building while the minerals remain.
Every three to four days, the water softener draws salt water from the brine tank to negatively charge itself again and release the positively charged minerals. These positively charged minerals are flushed out of the system through the plumbing system. In your case, they would flush through the septic system.

The Effects on Your Septic System

Water softeners have two potential consequences for septic systems: a system overload or clogging.
The flushing process we mentioned earlier happens almost twice a week. Each flush uses 50 and 150 gallons of salt water. This sudden influx of water can overload the septic system, especially if it happens at a time when your washing machine or dishwasher is running. The result can be water or sewage backups as well as an overwhelmed and flooding drain field.
Secondly, the brine water is especially harmful for the septic system because salt water is significantly heavier than fresh water. When the salt water enters the septic tank, it sinks to the bottom, sometimes even lifting the sludge and suspending it in the effluent along with the scum layer. This can allow sludge to flow out into the drain field, causing clogs in the pipes and foul odors in the field.