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Continuing to Classify Your Water


Dave Wilber

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I’ve really enjoyed the feedback I’ve gotten in the field and in email about the idea of looking hard at irrigation water. Thanks for that! And the really important thing I’m hearing is the need for understanding.  I’m doing this post from my iPad in the field, so please excuse the lack of monkeys.

Let’s continue for a quick look at three letters: TDS. Total Dissolved Solids is a really cool concept. I always have a hard time when someone says to me that water doesn’t have anything in it. It’s water, right? Well, wrong. That water has solids dissolved in the water column. We measure this in parts per million and it’s expressed sometimes in milligrams per liter… which is the same thing.

Here’s a general classification rule for water:

Fresh  less than 1,000 ppm TDS
Brackish  1,000-5,000 ppm TDS
Highly Brackish  5,000-15,000 ppm TDS
Saline 15,000-30,000 ppm TDS
Sea Water  30,000-40,000 ppm TDS
Brine  40,000-300,000+ ppm TDS

When someone starts telling me about their “saline” water, of course, we have to get on the right page for good conversation. In truth most of us are dealing with the first category and sometimes the second.

Here’s today’s fun take-away. These Dissolved Solids. They weigh something. Depending on what makes up the TDS of a water, that weight can be significant. A good water test will express this in pounds per acre-inch or pounds per acre-foot.

Three acre feet of water brings a nice application of 3,000 pounds of what is usually undesirable. A ten day stretch of big water nights brings about 15 tons of solids to your Turfgrass World.

Looking at a recent water test, I see  370.6 ppm of TDS which calcs out to just over 84 pounds per acre inch of water. So what? OK, let’s say that this particular 100 acre track gets a million gallons of water on a hot day. Just over 3 acre feet. My 84 pounds per acre inch turns into just over 1000 pounds per acre foot. Three acre feet of water brings a nice application of 3,000 pounds of what is usually undesirable. A ten day stretch of big water nights brings about 15 tons of solids to your Turfgrass World. Ten Days. 15 Tons. If this is your world, you better have a plan.

Now you know why I’m looking at TDS. In a future post, we will talk about what’s inside that big application you didn’t know you just made.


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