The traditional definition of hard water is water that contains a lot of minerals, such as:
Magnesium carbonate salts
Depending on the amount of these minerals and the type of plants you are growing, this type of hard water (e.g., well water containing many minerals) may be good or bad for plants.
Recently, the term has been expanded to include treated municipal tap water that contains chlorine, fluoride, and other chemicals.
This type of water is bad for plants under any circumstances because plants simply have no use for these chemicals, which may interfere with transpiration.
Suppose you believe you may have hard water. In that case, you can have it tested by your local agricultural extension, or if it is municipal water, just call your city hall or water superintendent to find out. [source]
Impacts Of Hard Municipal Tap Water On Plants
Hard municipal tap water may negatively impact your plants in several ways, including:
1. Scale Deposits On Leaves.
When you water overhead with a hose or sprayer or mist your plants with hard water, you are very likely to end up with a blotchy white film (limescale) on your plants’ leaves.
This coating interferes with light absorption and transpiration.
2. Leaf Color May Fade.
Having limescale on the leaves prevents light from getting in. This hampers photosynthesis, the process by which plants produce chlorophyll.
Chlorophyll is full of oxygen and nutrients and is responsible for keeping plant leaves the appropriate shade of green.
If the light is blocked and chlorophyll is not produced, your plants’ leaves will fade, and your plant will eventually die.
3. Salt Deposits May Build Up In Your Soil.
Very hard water containing a lot of calcium carbonate and other minerals may eventually leave a film of white mineral deposits over the soil’s surface.
This is especially problematic with container plants.
Salty soil is not supportive of planting growth and prosperity because it prevents plants from being able to uptake the water they need to survive and thrive.
4. Chlorine In Excessive Amounts Is Toxic To Plants.
When it is exposed to sunlight, it transforms into salt. When you expose your plants to this chemical repeatedly, it will not take long for them to weaken and die.
What Can You Do About Hard Water?
Depending upon the amount of watering you need to do, there are several options you may wish to pursue.
If you just have a few houseplants, purchase distilled water or spring water at your local grocery, collect rainwater, or water your plants.
If you have a clean spring nearby, you may wish to collect fresh water there but have it tested to find out if it is naturally hard or soft so that you can supplement your plants’ nutritional needs appropriately.
If you have a lot of houseplants, invest in reverse osmosis (RO) filtration system.
Just be advised that you will need to carefully supplement your plants with appropriate fertilizer because this kind of system removes all mineral content.
Rainwater collection is also possible for use in your yard and garden.
What If You Have To Use Hard Tap Water?
If you water your yard and garden with municipal water, chemicals will effectively dissipate into the open air.
Over time, you may have problems with mineral buildup in the soil if you do not have much rainfall.
When this happens, you will have to take steps to wash the minerals out and rebuild the soil.
If you must use hard tap water to water your houseplants, allow it to sit in a wide-mouthed container (e.g., a bucket) for 24 hours.
This will give chemicals a chance to evaporate and minerals to sink to the bottom of the container.
Don’t jostle or stir the container when you retrieve the water. Instead, use a cup or pitcher to dip the water from the top gently.
Leave a couple of inches in the bottom of the container.