Cover Story: Cultivation

Fundamentals of Water

Understanding the essentials of filtration and contaminants can help growers produce better crops

A high-quality product starts with high-quality water, which makes it imperative for growers to understand what they’re using to hydrate their crops.

Water-related pseudoscience comes in many forms, including magnetic water-conditioning systems, ionizers, alkaline water systems, living water systems and a variety of other scientific-sounding names.

People often use scientific terminology to deceive those without a science education. Conductive resonance, crystalline water structures, organized water, micro-water for easier digestion and others are all hocus-pocus.

Magnetic systems have been proven in laboratories to do absolutely nothing. Ionizers claim to create ions with anti-oxidant properties or even to make the water somehow living. (What do you want living in your water? Mold? Bacteria? Fungus?) Alkaline water systems have a small basis in science because they manipulate pH, but some make claims about their ability to cure cancer, diabetes, heart disease and a broad range of other ailments. Drinking alkaline water is like taking a Tums, in that it neutralizes some stomach acid, but little else.

Installation of industrial membrane devices water treatment based on reverse osmosis system

Contaminants

In order to understand the basics of water filtration, it’s important to take a deeper look at the particles floating amidst the water molecules. Air and water are the two primary transport mechanisms for nutrients and toxic contaminants. If your water has toxic chemicals, carcinogens, heavy metals, mold or fungus, then it’s likely your crop will too.

Water contaminants are generally divided into four categories: dissolved solids, suspended solids, organic contaminants and biological contaminants.

– Dissolved solids: This category includes all dissolved metals and ions in solution. Some of these may be healthy, such as calcium and magnesium, while others may be toxic, like arsenic and mercury. All metals have a positive charge. For every positively charged ion, there must be an equal amount of negatively charged ions — these include chloride and carbonate, as well as key components of fertilizers and hydroponic nutrients, such as phosphate and nitrate.

– Suspended solids: Suspended solids are bigger than single atoms or molecules. This can be confusing in that some things can be both suspended and dissolved. Have you ever put sugar into iced tea and watched it settle on the bottom of the glass? The sugar is a suspended solid, but if the tea is heated and stirred, the sugar will dissolve.

Common suspended solids include dirt, sand, leaves, twigs, silt and clays. Turbidity is a term used to quantify suspended solids. Just as TDS (total dissolved solids) does not specify which ions are dissolved, turbidity does not tell us what is suspended in the water, just that it is visually cloudy.

– Organic contaminants: In the marketing world, the word “organic” is used to refer to food or cannabis that is grown naturally without chemical herbicides and pesticides. In chemistry, “organic” contaminants are carbon-based dissolved constituents, including decaying plant and animal matter that may change the color or taste of water, but in most instances are not toxic. Other organic contaminants are frequently toxic, including industrial chemicals, components of gasoline and many herbicides and pesticides.

– Biological contaminants: These include mold, fungus, yeast, algae, bacteria and viruses. A common test for biological contaminants in well water is a total coliform test. There are many different types of coliform bacteria, including E. coli, which is a toxic product of human or animal waste. More than 40 million Americans use well water, which could potentially be cross-contaminated by a septic system. This would be shown in the total coliform test.

Many hydroponic growers have reverse osmosis systems with an atmospheric storage tank in the 50- to 1,000-gallon range. Some may believe that water is sterile, but it is not. Have you ever seen a swimming pool without chlorine that doesn’t grow algae? Probably not. It takes a tremendous amount of engineering, design and maintenance to keep a water system sterile or even close to sterile.

 

Treatment Concerns

Let’s start with a basic outdoor irrigation system and the treatment process. City-supplied water sources are easy to treat. If you get a water bill from your city, you have municipal water and that means it must meet Safe Drinking Water Act standards, governed by the U.S. Environmental Protection Agency. In a situation like this, users often install a centrifugal sand separator — a device that spins the water in a pipe so the sand falls to the bottom. This will prevent sprinklers from plugging with sand.

However, most people with properties that are one acre or larger have well water. There are many contaminants that can cause issues in well water or water that comes from lakes or rivers. It’s a good idea for growers to get a complete water test that includes dissolved metals and other ions, TDS, pH, organic chemicals and coliform bacteria.

Contaminants like iron and manganese are very common in well water and can be both suspended and dissolved. They will likely plug sprinklers, but they are not toxic and are classified as aesthetics. While city water is pH buffered to about 7.2, well water pH may not be ideal. Acids tend to dissolve metals, which is why hydroponic growers use water with a pH of below 7.0. This allows nutrients to dissolve, but also means the water cannot be run through copper or metallic piping other than certain grades of stainless steel. Sometimes alkaline water with a very high pH is used to strip biofilm in piping and water treatment systems.

Many greenhouses use reverse osmosis systems to treat their source water for plants and humidifiers. Water with a high mineral content causes deposits or scaling to form inside humidifiers and other equipment, requiring frequent cleaning.

Reverse osmosis uses a semi-permeable membrane with pressure applied to it. Reverse osmosis systems are often referred to as filters, but they’re actually separators that isolate concentrated minerals from pure water. The resulting product, or permeate water, is very close to being pure water.

Reverse osmosis systems are the most popular treatment choice for hydroponics because they start with pure water and growers can then add nutrients and maintain precise control over what they feed their cannabis plants, allowing for consistent, repeatable results wherever they set up shop.

 

Dan Saltsburg has degrees in environmental studies and geography from the University of California, Santa Barbara. He has worked in the water treatment industry since 1993. He is the owner of Big Brand Water Filter (www.bigbrandwater.com), which has sold water treatment products worldwide since 1998 and services many markets including agriculture, food and beverage, biotech and other commercial and industrial markets.

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