The Hard Truth about Soft Water

Salt… It’s a known killer but probably not in the way you think. Most of us know the health impacts of too much salt in our diets, such as heart disease, high blood pressure, and edema. Though few of us probably think about how salt from our water softeners may hurt our landscape plants.

“Hard water” is water containing large amounts of naturally occurring calcium, magnesium or other minerals. These minerals interfere with the cleaning power of household soaps and detergents by reducing soap’s ability to lather.  They react with ingredients in soap to produce a sticky scum which can cause plumbing problems.

Calcium and magnesium tend to be less water soluble than sodium and will “precipitate” or come out of solution as a pasty “scale”.  You may have seen evidence of scale as a white coating on the inside of your tea kettle, hot water heater, pipes or other containers which hold water. Scale impedes water flow through pipes and is a poor conductor of heat creating two undesirable situations for your household.

The byproducts created by water softeners are what can harm plants.  Most softeners contain several cubic feet of plastic resin coated with sodium ions. As tap water flows through the conditioner, the positive calcium and magnesium ions are “exchanged” with the positive sodium ions on the resin. They essentially switch places. The calcium and magnesium ions stick to the plastic resin and the sodium ions are released into the tap water. This is why softened water has a mild salty taste.

Eventually the plastic resin becomes loaded with calcium and magnesium and needs to be “recharged” with sodium. That’s where the sodium chloride pellets we buy come into play. Every few days, the water softener flushes out the hard minerals with a concentrated brine solution and replaces those minerals with sodium. The excess salts are discharged as part of household wastewater.

If landscape plants are watered with soft water, they can be “burned” by the sodium in the softened water. Symptoms of salt injury include stunted growth, yellowed foliage and leaf margins which begin to curl and turn brown. These symptoms are similar in appearance to drought stress and can be easily misinterpreted in our arid environment.

So what to do? Fortunately most professional installers are aware that water for outside use needs to remain separate from household water and they take the necessary steps to keep them apart.  Occasionally this separation step gets bypassed. In such cases, homeowners concerned about their landscape plants can switch to potassium chloride as their water softening salt.  Potassium is a macro-nutrient that plants need and won’t harm plants like sodium.

While at the Water Wise program, I perform residential on-site visits and was often asked whether it is important to separate soft water from outside spigots. Many of these visits were for people just moving to Arizona from moister states and they are not familiar with our dry climate. My response was usually very simple. Moist locations have a lot more precipitation than we do which helps flush salt out of the soil and away from plants, minimizing damage. Here salts build up in soils.

Does this mean you shouldn’t use water softeners? No, but it does suggest you need to have a better understanding of how your plumbing should complement your plants. Before installing a conditioning system, get details on how it will be installed and be sure the installers know about your landscape needs.

If you already have a system installed that does not separate inside and outside waters, consider switching to potassium chloride as your water softening salt. Your plants will thank you if you do!

 

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