You know where I tasted the best tap water? ARUBA! ...an island off the coast of Venezuela. Why? The island desalinated the seawater by distillation from the heat of their electric power plant. Smart, right?! The water came out of the tap distilled!
When evaluating your grow, water quality is an important topic. Is it from a city water supply or a well? How is your water treated? What's the TDS out of the tap? Is the water put through a water softener? Are you utilizing filtration systems? What kind of filtration?
In this article, I talk about Total Dissolved Solids, Reverse Osmosis Filtration, Well Water, Water Softeners, and Water Treatment. The last topic, water treatment, is a must-read for everyone, even if you skim past the first topics.
Total Dissolved Solids (TDS)
TDS refers to the total amount of dissolved substances—mineral or otherwise—present in your water. In gardening, we estimate TDS using conductivity meters. These meters use two metal probes and send a small electrical current between them; a built-in processor measures how well the water conducts electricity and converts that reading into either TDS or Electrical Conductivity (EC). Most meters include calibration controls and let you switch between TDS (ppm) and EC (mS or µS), depending on your preference.
The units of measurement depend on the meter and the user's preference. TDS values are conventionally in "parts per million" (ppm), a value that is roughly equivalent to milligrams per liter (mg/L) of solution. Alternatively, you can track the amount of minerals based on the conductivity in units of Siemens or, commonly, millisiemens. Learn about the different conductivity scales, check out Bluelab's article, "
I recommend cloning with water below 200 ppm on the 500 scale before adding nutrients. That is 0.4 millisiemens (mS) conductivity or 400 microsiemens (uS). Once you add nutrients to your water, these values will increase depending on the strength of the nutrients. Owning an EC or TDS meter lets you monitor your water quality and nutrient levels.
I personally log conductivity in microsiemens (uS) which is 1/1000 a millisiemen (mS). For customers, I often speak in terms of the more common hydroponic units: millisiemens (0.002 - 3.0 mS is usual) or ppm (1 - 1500 ppm is a standard range). I have operated grows with water supplies ranging from 60 ppm to 3000 ppm. The two higher values were 500 and 3000 ppm and were on rural wells tapping aquifers linked to limestone. These high TDS values out of the tap required filtration.
When it comes to cloning, if your water is above 200 - 300 ppm I recommend Reverse Osmosis Filtration (discussed next). If your water is under 200 ppm, jump to Water Softeners and Water Treatment. For cloning and hydroponics it is a must that everyone read about Water Treatment.
Reverse Osmosis Filtration (RO):
Reverse osmosis pushes your water through membranes with pores so small that ions cannot easily pass through, BUT most of the water can. There's a small amount of water that can't make it through referred to as 'brine' and contains the molecules and ions too big to make it through the RO membrane. Usually, the brine tubing from your RO is black or another color to indicate it contains unwanted water. I recommend using that brine to water your grass, top off swamp coolers, or other application as opposed to dumping it down the drain. Installing an RO can seem daunting, but it's easy. If you're overwhelmed, work closely with the tech support of the manufacturer.
With RO filtration, if the source mineral content is high, your RO system (within a few uses) will only reduce mineral content by 90%, leaving 10% residual. For example, if your water source is at 500 ppm, you may end up with 50 ppm residual mineral content. If a water softener is employed, that is about 50 ppm of sodium (Na+) ions. I discuss Water Softeners in the next section, along with an options to eliminate sodium in these systems.
With your RO system, you can prevent this increase to 10% by changing your ion-exchange column (also referred to as a Mixed Bed Ion Exchange column). Simply change out the last column every time the TDS jumps back up to the 10% value mentioned above. Some mixed-bed ion exchange resins have a color indicator that changes color when saturated.
Water Softeners
Water softeners swap calcium ions for sodium ions. This is to protect your home appliances because sodium salts are very soluble and will not leave mineral deposits. While calcium (and other minerals) can leave deposits and build up in appliances. The problem is that sodium (Na) is not an essential mineral for plant nutrition or hydroponics. In high amounts, sodium will antagonize or compete for uptake certain nutrients, such as potassium (K). If you use a softener, take note of the TDS/EC of Sodium after the filter. If you're above 50 ppm, you may consider regularly exchanging your Ion Exchange Column on your RO OR switching to potassium salts (KCl) in your water softener. Using potassium salts would make your RO flow-through potassium (K) instead of sodium (Na). Bags of Potassium softener salts are generally sold where sodium softener salts are available.
Water Treatment
By now, you have water with minerals below 200 ppm (or 0.4 mS TDS), AND the mineral content is plant-safe (i.e., Calcium or Potassium). The next topic is water treatment. In cloning, we prefer water treatment, while the results vary from city to city. For example, I found a suburb in Dallas, TX with ~4 ppm free chlorine on pool test strips. This is near levels recommended for swimming pools.
Meanwhile, in Austin, TX, the readings were undetectable. You can use chlorine test strips from a local pool supply store to determine your water's treatment level. I like the pool test strips that tell you pH, alkalinity, total chlorine, and more. They're a great sanity check for all your instruments.
If you have tap water below 4 ppm Chlorine or undetectable free chlorine, I recommend boosting your initial cloning water to 4 ppm chlorine. This is even more important if you're using well water. Here's the recipe:
0.10 - 0.20 mL/gal of Bleach® (8.25% sodium hypochlorite) yields approximately 2 - 4 ppm of free chlorine and an ideal dose range for UNROOTED cuttings.
1 mL = 20 drops; so 0.10 - 0.20 mL is 2 - 4 drops of 8.25% Sodium Hydrophlorite (Bleach®)
ALWAYS add oxidizing products BEFORE pH adjustment OR additives. “free chlorine” reacts with most hydroponic additives. Be sure to expose clean pH and TDS meters to this solution before adding your nutrients and additives to surface sterilize. Then, after all your cuttings are in place, I recommend a second boost of chlorine at 4 ppm (4 drops/gal OR 0.2 mL/gal) to surface sterilize your cuttings and sterilize any surfaces you contacted while filling the cloner.
Hypochlorous Acid products like Watermax™, Clear Line™, and Clear Rez™ are effective at 10x – 100x lower chlorine concentrations than hypochlorite salts such as Pool Shock (calcium Hypochlorite) or Bleach (Sodium Hypochlorite). Hypochlorite products are NOT the same as Hypochlorous acid products. Hypochlorite products (such as pool shock or bleach) require 0.5 – 5 ppm free chlorine to effectively sterilize plant root systems or cuttings, while Hypochlorous acid is effective at 0.05–0.5 ppm.
What I like about working with hypochlorite salts (Pool Shock & Bleach) is I can use inexpensive pool test strips to help verify I am in the 2 - 4 ppm free chlorine range. AND REMEMBER, all low-dose oxidizers (including hydrogen peroxide) should be added before and AFTER ALL cuttings are in place, BUT ALWAYS before nutrients or additives. This ensures their oxidation potential is focused on your system and cuttings. While Nutrients and additives cross-react with oxidizers, lowering their effectiveness.
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