Recycled water in home landscapes

The trouble with reclaimed water

Last year during the summer I saw a lot of trucks hauling reclaimed water from the local water treatment plant. Free water! = great idea! = not so much? = maybe even no.  I have to admit, I had never thought of using reclaimed water in my landscape.  I prefer the good stuff from up above, and don’t need that much of it anymore. Plus, hauling a big tank around doesn’t seem ideal for a long term plan.  Then a friend of mine reminded me that it has a lot of salt.  Yikes!  If you need to use it to get by on the short term here’s what I would do:

  1. know your plants and whether or not they are salt sensitive
  2. ask the treatment plant if they have done any analyses on it
  3. get it tested yourself so you know what you are dealing with
  4. water very DEEPLY and less often

Deep watering is a must

Salts move through the soil along with the wetting front. That means if you water shallowly (not past the root zone) salts will accumulate in the soil as far as the water reaches. If this is in or near the root zone, it can stress the plant.  A lot of people who think they have a brown thumb when it comes to indoor house plants, often water their plants too shallowly and never flush the soil thoroughly so that the water runs out the bottom of the pot.  After a couple months the leaf tips start to turn brown. This is because the salts in the fertilizers never get moved out and the salts in the water (tap water has salts too) you are applying accumulate, compounding the problem.  The same principle applies to plants in ground, water really needs to move past the roots to encourage deep rooting and flush out contaminants like salt.  How do you know if you have watered deeply enough?  In compacted clay soil (which is what is very common in the east bay) water tends to move out first, rather than move down.  Watering slowly promotes better saturation at good depths.  The only way to know is to dig down near the plant after watering and check or you can use a moisture meter.

Gypsum is usually helpful

If someone tells you to add gypsum to your soil to alleviate the salt it ‘might’ be a good idea.  When you add gypsum to a soil it does two important things. First, the calcium in the gypsum replaces a lot of the sodium ions on the cation exchange sites.  Second, the sulfate in the gypsum binds with the sodium to form sodium sulfate. Sodium sulfate is highly water soluble and it can be easily flushed from the soil.  The importance of this is that these reactions work with sodium, but not all salts are sodium salts.  There are others such as magnesium, potassium, and boron. You can’t know what is in the water unless you ask or get it tested.  Using too much gypsum could adversely affect your soil by creating a calcium / magnesium imbalance.

Is using it okay?

In general, I think it’s okay to use reclaimed water on salt tolerant plants if you water deeply.  I’d also back off on the fertilizer if you use it.  If you notice your plants or trees are declining, get your soil tested. It’s so easy to do. For $35.00 you can get a ton of information that a good lab or gardener can interpret for you.