The Disadvantages of Reverse Osmosis in Agricultural Applications

August 30, 2019

Reverse osmosis is an effective way to purify water, but presents serious shortcomings in agriculture and other applications with large-scale water demands.

Reverse osmosis is a time-tested means of purifying water at scales ranging from residential to industrial, for a variety of applications including manufacturing, agriculture, and human consumption. Regardless of the size of the reverse osmosis system, the process is largely the same: pressure is used to force water through a membrane with pores so small that water can pass through, but bacteria, viruses, and molecules of contaminants like heavy metals are left behind.

This approach is very effective at purifying and decontaminating water. However, reverse osmosis presents serious shortcomings that become increasingly obvious as the scale of water demand increases.

Reverse osmosis systems are labor intensive and costly to maintain, especially the membranes.

Of the most maintenance-intensive elements of a reverse osmosis system is the filter. The holes in the filter are incredibly tiny—only about one ten-billionth of a meter across. For comparison, the thickness of a piece of paper is about a million times greater.

It shouldn’t come as a surprise that the membranes frequently become clogged, especially when the water source is of a lower quality. When this happens, the membranes must be cleaned frequently. Failing to appropriately clean and maintain a reverse osmosis membrane can result in bacteria growing through the membrane, which compromises the filtered water. Mineral buildup can also occur, and during a cleaning cycle, the cleaner used will react with the minerals and eat holes in the membrane, irreparably damaging it.

Regardless of how well you maintain the membrane, it will still have to be replaced. When well maintained and used with a higher quality water source, a membrane may last about five years. But the performance of a membrane has to be monitored, and it may have to be replaced earlier than anticipated if it no longer meets filtration specifications.

Replacing a single membrane in a larger scale system typically costs $2,000 to $3,000. With industrial-scale systems, membrane replacement costs are significantly higher. Industrial scale systems rely on multiple membranes—anywhere from 3 to dozens—and replacing a set of 3 membranes can cost $10,000 when factoring in parts, labor, and lost productivity.

It should also be noted that the performance of reverse osmosis membranes can be compromised by water sources or operating conditions with inconsistent temperatures. In warmer water conditions, the pores of the membrane will expand, allowing larger particles to pass through. In cooler conditions, the pores will shrink and filter out smaller contaminants, but will also make the pump work harder.

Membrane replacement isn’t the only significant maintenance cost associated with reverse osmosis systems. The pump that generates the pressures needed to force water through the membrane requires occasional servicing, due to the wear and tear from running the system.

Immense amounts of waste water are generated by reverse osmosis systems, and sometimes this waste water must be disposed of in a manner complying with state and federal regulations.

For a reverse osmosis system to generate pure water, it must ‘reject’ a certain amount of water, depending on the application and desired quality of water. Reverse osmosis systems used for agricultural irrigation can generally be set to reject much less water than a system used for industrial applications. But the amount of wasted water is still quite high.

Let’s say that a reverse osmosis system produces 1 gallon of waste water for every gallon of purified water it produces (in many cases, this is a pretty conservative estimate). This level of waste doesn’t pose an issue for the average homeowner. But in agricultural applications—whether you’re irrigating crops in the field or supplying water to an indoor hydroponics system—this level of waste is immensely costly. For every gallon of purified water produced, you’re dumping a gallon of water. This is unsustainable for many growers, especially those that have limited water allotments.

Then there’s the matter of disposing of the waste water. Depending on the water source, waste water produced by a reverse osmosis system can be dangerous. For instance, if the salt content of the water source is high, the waste water will have potentially toxic levels of salt and may require processing before it can be discharged. Other contaminants can be a serious problem as well. We have personally worked with a client with a well that has levels of arsenic higher than the EPA’s safe limit. Using a reverse osmosis system with this water source would be unwise, as the waste water would have higher levels of arsenic, and be a major liability for the well owner.

Water processed by a reverse osmosis system is stripped of numerous beneficial minerals and has an acidic pH.

While reverse osmosis is great at removing harmful contaminants from water, it also strips out all other minerals. When water from a reverse osmosis system is used for irrigation, it leaches minerals out of the soil or growing media, including calcium and other minerals critical to healthy plant growth. This creates additional costs for growers, as the lost minerals must be supplemented.

Ensuring ideal growing conditions is complicated by the fact that reverse osmosis lowers the pH of processed water to as low as 5 (neutral pH is 7). This presents a problem, as plants generally prefer a pH of around 5.5 to 7. Dropping below that 5.5 level results in nutrients leaching, which of course exacerbates the leaching that occurs due to the mineral-free nature of reverse osmosis-derived water.

Reverse osmosis does not remove all bacteria, viruses, and fungal spores.

The reverse osmosis process is very efficient at removing a wide variety of contaminants, including pathogens. However, it is not 100% effective. A very small percentage of microorganisms may pass through the membrane due to manufacturing imperfections (which is why manufacturers are  careful to not guarantee the removal of all pathogens).

In addition, damage or failure of seals can allow small amounts of water to pass through the system untreated. For growers who need to eliminate potential fungal contamination—especially cannabis growers, who work in warm environments highly conducive to fungal and mold growth—this presents a serious problem.

For growers and other businesses that need a better water purification solution, ozonated water systems offer a solution.

Watson Well has been around for many years, and in that time, we’ve had the opportunity to speak with countless clients about their many different types of water purification systems, including reverse osmosis systems of all sizes and types.

Reverse osmosis is a perfectly acceptable way to deliver small amounts of purified water for home use. However, its extreme inefficiency and high cost of use poses serious problems for users with large-scale needs. We have had the opportunity to work with growers and other commercial users who were extremely frustrated with their systems,  blindsided by the shortcomings and additional costs of reverse osmosis.

This is why we take a different approach to large-scale water treatment, with our ozonated agricultural water treatment systems. Rather than relying on costly, service-intensive filtration membranes, our systems use high levels of ozone to kill all pathogens in the water, while oxidizing (and neutralizing) heavy metals and other contaminants.

The result is a water treatment solution that requires far less maintenance, is cheaper to operate, and can deliver a far greater flow rate than comparable reverse osmosis systems. We invite you to take some time to learn more about ozone water treatment, or contact us today to learn how we can help you meet the water needs of your farm, business, or agricultural operation.

California Groundwater Association
National Groundwater Association