Interpreting a Water Report: How to Make the Most of the Information You Have.

Photo courtesy of Freedigitalphotos.net

So you have been reading my blogs and now before you sits a water quality report! Are you asking yourself “now what?”  It says you have a pH of 6.84 and a Alkalinity of 37.3… is that good or bad?  Well read on my friends as we delve deeper into deciphering a water report.

pH: Potential of Hydrogen.  It is the measure of the concentration of hydrogen ions (H+).  pH is measured on a logarithmic scale of 1-14; 1 being most acidic & 14 being most alkaline.

  • Acceptable range is 6.5-8.0
  • <6.0 or >8.0 can cause severe problems
  • pH influences the availability of plant nutrients and other elements.

Alkalinity: Think of this as the ability of water to neutralize acid.  The higher the alkalinity the more acid it will take to lower the pH of the water.  Alkalinity is a measurement that incorporates the amount of bicarbonates, carbonates, and hydroxides joined to calcium, magnesium, & sodium.  Alkalinity is expressed in parts per million (PPM) of Calcium Carbonate (CaCO3.)

  • Anything above 120 PPM CaCO3 may cause a gradual increase in the pH of your potting medium.
  • Low Alkalinity water (less than 60 PPM CaCO3) is not able to neutralize sufficient amounts of acid as such the recurrent use of acidic fertilizers may result in a decrease in the pH of your growing medium.

Electrical Conductivity (EC): A measure of the conductivity of a solution.  As the level of mineral salt dissolved in the water increases so does the solution’s conductivity.  EC is often expressed in mhos (reciprocal ohms.)  Most water reports express EC in the smaller unit mmhos/cm or millimhos per centimeter.

  • Acceptable range is 0.5-0.75 mmhos/cm
  • Problematic range is 0.76-3.0 mmhos/cm
  • The severity of the problem will be determined by two factors:
    • What compound is responsible for the elevated EC?
    • How high the EC is.

Sodium Absorption Ratio (SAR): is a measure of the suitability of water for use in agricultural irrigation. It defines the sodium (Na) hazard by comparing the concentration of sodium to the concentration of Calcium and Magnesium.  A High SAR value can cause reduced porosity in soils and create a “salt crust” on the surface which will prevent water from being absorbed by the soil.  Fine soils (i.e. clays) are affected more than large particle soils (i.e. sandy soils.)

  • Acceptable range is <10 mEq/L
  • Problematic range is 10.1 – 18 mEq/L
  • Severe problem range over 18 mEq/L
    • (mEq/l is short for milliequivalents per liter)

Phosphate (PO4-P): Commonly found in groundwater and fertilizers.

  • Acceptable range is <1.2 ppm
  • Problematic range is 1.2 – 2.4 ppm
  • Severe problem range over >2.4 ppm
    • Too much phosphates can cause algal blooms in runoff water followed by significant decrease in dissolved oxygen
    • Manage with reverse osmosis filters or build fertilizer program around the levels in your water supply

Potassium (K+): Originates from dissolved rock, soil, and fertilizer.

  • Acceptable range is <20 ppm
  • Problematic range is 20 – 50 ppm
  • Severe problem range over >50 ppm (can cause foliar damage)
    • High levels can increase levels of Potassium in plant tissue thereby creating nutrient antagonism of Nitrogen or Magnesium
    • Manage with reverse osmosis filters

Calcium (Ca+2): Originates from dissolved rock, limestone, gypsum, soil, or fertilizer.  High levels of calcium form lime deposits when combined with CO3 or HCO3.

  • Acceptable range is <25 ppm for soil and water hazard but <60 ppm for ideal foliar levels
  • Problematic range is 25 – 250 ppm for soil and water hazard but 60 – 100 ppm for problems with foliar injury
  • Severe problem range over >250 ppm for soil and water hazard but >100 ppm for severe foliar injury

Magnesium (Mg+2): Originates from dissolved rock, limestone, dolomite, soils, and fertilizers. High levels of magnesium form lime deposits when combined with CO3 or HCO3.

  • Acceptable range is <20 ppm
  • Problematic range is 20 – 40 ppm
  • Severe problem range over >40 ppm

*When designing a fertilizer program remember the ideal ratio of K:Ca:Mg is 4:2:1

Zinc (Zn):  Occurs naturally in small amounts.

  • Acceptable range is <2.0 ppm
  • Problematic range is >2.0 ppm

Copper (Cu): Occurs naturally in small amounts but may be present due to corroding copper pipes.

  • Acceptable range is <0.2 ppm
  • Problematic range is 0.2 -5.0 ppm
  • Severe problem range over >5.0 ppm
  • Toxicity in some plants has been shown with levels as low as 1.0 ppm.

Manganese (Mn): Dissolved from shale and sandstone, not usually a problem.

  • Acceptable range is <0.2 ppm
  • Problematic range is >0.2 ppm

Iron (Fe+2 or +3):  Iron is the 4th most abundant element in the earth’s crust.  Not easily absorbed by plants unless the pH of the water is less than 5.5.  Iron can mix with bacteria causing slimes which can clog irrigation equipment.

  • Acceptable range is <0.3 ppm
  • Problematic range is 0.3 -5.0 ppm
  • Severe problem range over >5.0 ppm
  • Levels greater than 5.0 ppm can form coatings on leaf surfaces reducing photosynthesis.

Sulfate (SO4-2): Naturally dissolved into water from rock and soil containing gypsum, iron sulfides, and other sulfur compounds. If mixed with calcium scale can form.

  • Acceptable range is <100 ppm
  • Problematic range is 100-200 ppm
  • Severe problem range over >200 ppm
  • Reverse Osmosis filtration is recommended course of action if levels are high.

Boron (B): Naturally occurring from ground water and decaying plant material.  Boron is required in small amounts, when in excess it is highly toxic.

  • Acceptable range is <1 ppm
  • Problematic range is 1.0-2.0 ppm
  • Severe problem range over >2.0 ppm

Sodium (Na+): Naturally occurring from dissolved minerals but also from road-salt & fertilizer.  Levels Greater than 70 ppm can cause foliar damage (leaf burn.)

  • Acceptable range is <70 ppm
  • Problematic range is 70-200 ppm
  • Severe problem range over >200 ppm

 Chloride (Cl-): Naturally occurs from dissolved minerals and sea water, but also may come from road-salt, fertilizer, and sewage.  Levels Greater than 100 ppm can cause foliar damage (leaf burn.)  Chloride can be absorbed by plant roots accumulating in leaves causing toxicity.

  • Acceptable range is <70 ppm
  • Problematic range is 70-300 ppm
  • Severe problem range over >300 ppm

 Nitrate (NO3-N): Naturally occurring in soil and from decaying plant material, high levels are often the result of fertilizer usage.  High concentrations can cause plant tissue to become more susceptible to pests.

  • Acceptable range is <50 ppm
  • Problematic range is 50-100 ppm
  • Severe problem range over >100 ppm

4 thoughts on “Interpreting a Water Report: How to Make the Most of the Information You Have.

  1. hello,
    thank you for these information, but what is the good value of temperature and humidity to keep in the room to avoid a bacterias
    thank you for your help

    • Hello and thank you for your comment. The ideal temperature and humidity are going to be dictated more by specific crop, then by desire to keep bacterial populations down. Generally ideal temperatures for the majority of plants will be between 70-85 degrees Fahrenheit and a humidity range of 50-60%.

  2. So I guess I can either set up a complete water testing lab–or simply do a drain and fill of my water reservoir: with price of chemical on a lager scale testing might be the way to go// wondering how the new Gro-bot would handle this. Would but do a flush and fill or just add it what chemicals are needed. I see it will adjust ph on its own. Trying to understand the scope of the whole issue. Thanks

    • Hello Al,
      A water test is a one time necessity to understand the mineral content you are working with. After that, it is up to the grower to decide if it is worthwhile on a regular basis. As far as regular reservoir changes go, I recommend you change them every 7-10 days for hobbyist systems and every 10-21 days for commercial systems (500 gallons plus). The GroBot is a great machine and can be utilized to perform your reservoir changes automatically but it can not inject individual elements into a solution only fertilizer solution concentrates. If you have further questions please let me know. Best Regards.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s