By Rehan Iqbal
Why do some areas ban the use of water softeners? Why are some water softeners banned, and others aren’t? It's all due to recharging. Ion exchange filters need to be recharged once or twice a week with salt water. This water causes all kinds of ecological damage when it goes down the drain. How do you work around these issues, so you can protect your water supply and stay on the right side of the law?
In 2020, there were 10 million residential softeners and about 60,000 industrial softeners in use across the U.S. These softeners are only used in places with hard water, with the highest concentration in California. In this state, between 20 and 25% of homes have water softeners. A single household system discharges around one pound of salt per day, and between 70 and 300 gallons of salty water per week. When you have lots of homes using these systems, salinity quickly becomes an issue.
Ion exchange systems reduce water hardness by replacing calcium and magnesium ions with sodium ions. When the sodium ions in the media tank are used up, the system needs to recharge. Sodium chloride or potassium chloride is mixed with water, then forced through the tank.
The sodium in this brine swaps places with the trapped hard water ions. This process isn’t 100% efficient, so the resulting water still has a high salt content. This is especially true of brine used before the softener tank is fully saturated with minerals. Any salt that can’t react with calcium and magnesium on the filter media is flushed out.
Brine contains at least 50,000 mg/L of sodium. For comparison, sea water is around 35,000 mg/L, groundwater contains between 200 to 10,000 mg/L, and freshwater in lakes, streams and rivers is under 1000 mg/L. It doesn’t take much brine to raise the salinity of groundwater, streams, lakes and rivers.
Salt has high osmotic potential. If you have a reverse osmosis filter, you may be familiar with osmosis. If you put a permeable barrier between clean water and salty water, the clean water will cross the barrier until both sides have the same salinity. Water treatment devices use pressure to reverse this process, creating salt-free water.
However, that pressure doesn’t exist in nature. Once brine enters the groundwater, osmosis mixes it with fresh water, raising the salinity over a large area. Osmosis draws moisture away from plants, causing a physiological drought. Sodium also displaces other nutrients, which affects plant growth.
Salty water is better at moving soil aggregates than freshwater. This force destroys the soil’s structure, reducing its permeability. In turn, this makes the water table smaller, permanently reducing the water available to plants.
Chlorides are toxic to aquatic life, greatly reducing reproductive rates in several species. While runoff from road salt is the main source of chloride pollution in northern states, softener runoff is a major pollution source in areas requiring hard water treatment.
To protect aquatic life, chloride levels need to stay below 230 mg/L. A study conducted by the United States Geological Survey in 2009 found that over 40% of urban streams were over this limit. This prompted local and state governments to limit the release of chloride-containing products into the wild, including brine from ion exchange water softeners.
Not all devices marketed as water softeners create salty water. However, it’s more correct to say that not all solutions for treating hard water are banned.
Salt-free systems use nucleation instead of ion exchange to deal with minerals. When you were in school, you may have made rock candy in science class to observe crystal growth. Once you put sugar on the stick and place it in a sugar solution, the dissolved sugar latches onto the solid sugar, growing crystals.
The same principle is at work in these conditioners. The media inside the tank has places for hard water ions to bond to. This kicks off a chain reaction, drawing in more ions, which bond together to form crystals. Eventually, these crystals get too big to stick to the media, and they flake off.
These flakes of microscopic calcium and magnesium are inert, so they don’t form scale and they don’t react with soap. Since the minerals are still in the water, the water is still hard. It just doesn’t cause the same problems as regular softened water.
Currently, there is a state-wide ban on these softeners in Texas, unless they meet strict criteria on brine production. Areas of California, Connecticut, Wisconsin, Michigan and Minnesota have also banned water softeners.
Nucleation systems have their limitations. Until recently, there weren’t many systems out there that could handle water with a hardness greater than 10 GPG. Ion exchange is also be used to remove other contaminates, like lead and arsenic. Innovations like metered valves, which only regenerate media after a certain amount of water is used, reduce brine waste. These devices are still legal in areas that don’t have environmental problems with chlorine and salt.
For most water sources, all you need to do is change the tanks. Your water won’t feel as slick, since it doesn’t contain salt. Otherwise, you probably won’t notice any major changes. The nucleation process also forms microscopic carbon dioxide bubbles.
If your home didn’t always use a water softener, the these bubbles will scrub off any limescale on your pipes. This will increase the hardness of your water until the pipes are clean. For homes with heavy limescale, this process takes as long as 9 weeks.
While nucleation filters only work on calcium and magnesium, ion exchange works on all types of metals, including lead. If you have heavy metal contamination, you need to add a catalytic carbon filter to your water treatment system. This filter absorbs metals that were previously removed by your salt-based water softener.
These exchange services are touted as an alternative to stand-alone home water softeners. They use ion exchange systems, so they’re still salt-based. However, recharging isn’t done on site. Instead, the media tank is swapped out every few weeks. The used tank goes to a facility for recharging, and the brine is disposed of in a way that doesn’t threaten ground water supplies. This is a great alternative to a standard ion exchange system, giving you all the benefits without the pollution or legal issues.
In the future, we’ll still have these water softeners, but they’ll have a recovery system to reduce the amount of salt that enters the ground water. The IAPMO, an organization that works on international plumbing regulations, has set up a group to do more research into these systems to bring them to market.
These recovery systems have a holding tank fitted with a filter that’s similar to what you’ll find in a RO system. This lets water and most minerals pass through, while trapping salts. This concentrated brine goes back to the brine tank for reuse.
Experimental systems can filter out 75% of the salt in the brine, and they reduce the water used to recharge systems by 35-40%. While the purchase price for these filters will be higher, operating costs will be significantly lower.