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An Overview of Reverse Osmosis and Distillation Systems

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An Overview of Reverse Osmosis and Distillation Systems

What is Reverse Osmosis?

Reverse Osmosis is a water purification process that uses pressure to force water through a semipermeable membrane. It is commonly used during the production of bottled fresh water and the desalination of salt water.

Reverse Osmosis is also a common step in many household water purification systems. Such systems typically include:

  • A sediment filter
  • An activated carbon filter
  • A Reverse Osmosis membrane
  • An ultraviolet lamp for sterilizing microbes that escape filtration

The systems are typically installed under a sink, and pull in water from an incoming tap line.

Understanding Osmosis

Osmosis is the, “Tendency of water to flow from a hypotonic solution (low concentration of dissolved substances) to hypertonic solution (higher concentration of dissolved substances) across a semipermeable membrane.”1

Think of a tank of water with two chambers. One chamber has a low level of dissolved substances (salt, bacteria, or contaminants), while the other chamber has a high level of dissolved substances. Water would naturally flow through a semipermeable membrane toward the chamber with the higher level of dissolved substances in order to even out the concentrations between the two chambers.

RO Uses Pressure to Control the Flow of Water

Reverse Osmosis pressurizes the solution with the higher level of dissolved substances in order to reverse the natural flow of osmosis. It forces water to move toward the chamber with the lower level of dissolved substances, resulting in filtered water accumulating in the second chamber.

What can I expect from a Reverse Osmosis system at home?

Typical Performance / What a Home System Removes

At-home Reverse Osmosis systems are capable of removing up to 99%+ of dissolved salts (ions), particles, minerals, organics, bacteria and cysts (such as cryptosporidium) from incoming tap water.2 They also reduce certain tastes, some pesticides, high chloride content, nitrate, heavy metals, and arsenic.3

While models of Reverse Osmosis systems will vary, in general several categories of contaminants should be considered carefully when evaluating effectiveness: dissolved gases, trihalomethanes, VOCs and bacteria.

According to Cornell Cooperative Extension, College of Human Ecology:

Reverse osmosis will not remove all contaminants from water. Dissolved gases such as oxygen and carbon dioxide pass through RO membranes into the treated water. Unfortunately, hydrogen sulfide gas, with its notorious odor of rotten eggs, also passes through the RO membrane. RO in general is not a very effective treatment for trihalomethanes (THMs), some pesticides, solvents, and other volatile organic chemicals (VOCs). However, RO systems can be certified by NSF for VOCs, THMs, and several pesticides and solvents if the contamination is not too high.4

Bacteria Reduction and Tank Colonization

Reverse Osmosis systems often add a UV light to the system in order to more effectively reduce bacteria.5 However, the UV light sometimes does not kill all the bacteria because any turbidity in the water can create shaded spots, preventing some bacteria from being exposed. In addition, the UV is installed before the bladder tank; however it is in the bladder tank that bacteria usually colonize. Therefore, if the bladder tank is not sterilized on a regular basis, it becomes a source for bacteriological contamination. Note that the carcasses of the dead bacteria may remain within the bladder tank (the filtered drinking water) with a Reverse Osmosis system.6

Maintaining a Traditional Reverse Osmosis Systems

Reverse Osmosis systems can have up to four filter elements, with each needing to be changed at various intervals ranging from four months up to two years. This process may require that water pressure to the home be shut off, and part or all of the system be disassembled for maintenance. Additionally, the bladder tank should be washed with a chlorine solution at six-month intervals to kill any colonizing bacteria.7

Maintaining a Tankless Reverse Osmosis Systems

While some newer tankless Reverse Osmosis systems have overcome the issue of bacteria colonizing in the bladder tank, these systems have their own set of inherent issues, including:

  • TDS Creep: without a flush tank, the initial water coming out can taste horrid, due to increased TDS in the water. TDS creep is common to all systems using an RO membrane and results from the natural diffusion of TDS ions through the membrane from the feed side to the permeate side when the tank is full. This results in lowered or “dirty” water quality.
  • High Failure Rate: some tankless models have already been removed from the market, due to numerous issues, including high rates of failure. Noise: depending on the specific model and features, some units are extremely noisy to operate.
  • Excessive Water Waste: this is a problem with both standard and tankless Reverse Osmosis systems.
  • Cost: with multiple membranes being used, the overall cost per gallon, can be even more expensive than older-style Reverse Osmosis systems.

In an Emergency

Here are several items to consider regarding relying on a Reverse Osmosis system during an emergency:

  • They require electrical power to function, which may not be available
  • They require water pressure to function, which also may not be available
  • They are not portable, and cannot travel with you during an evacuation
  • They are typically suggested for use only with “biologically safe” water sources

What is distillation?

Distillation is the process of purifying water through boiling the water and collecting the steam. When water is purified by distillation, it is boiled in a container and the steam is sent into cooling tubes.10 The steam is condensed and then collected as purified water in a second container. The impurities in the water are left behind in the first container and can be discarded. Distillation is used for many commercial purposes, including the production of gasoline, distilled water, alcohol, paraffin, kerosene and many other liquids.

What can I expect from a distillation system at home?

Typical Performance / What a Home System Removes

Distillation removes sediment, high salt content, high total dissolved solids, pesticides (if properly equipped with a gas vent), fluoride, nitrate, lead, copper and other heavy metals, arsenic, and bacteria.11 Depending on the system, and if operated properly, it may also effectively inactivate microorganisms such as bacteria, cysts and viruses.12

Distillation does not remove chlorine, chlorine byproducts, some VOCs, certain herbicides and other chemicals with boiling points lower than or near that of water.13 Contaminants that easily turn into gases, such as gasoline components or radon, may be retained in the water unless the system is specifically designed to remove them. In addition, bacteria may recolonize on the cooling coils during inactive periods. Distillation also removes beneficial minerals from the water.

Maintaining Distillation Systems

Water distillers range from relatively small countertop units to large floor models for commercial and industrial use. At-home distillation units typically consist of:

  • A boiling chamber, where the water enters, is heated and vaporized
  • Condensing coils or chamber, where the water is cooled and converted back to liquid water
  • A storage tank for purified water

Distillation systems need to be cleaned with a vinegar solution regularly to remove scale buildup. The distilled water holding tank should also be disinfected periodically. For those with hard water, a water softener may reduce the frequency of required cleanings.14 Keep in mind this will add salts to the water. Unevaporated pollutants remaining in the boiling chamber need to be regularly flushed to the septic or sewer system.

In an Emergency

Here are several items to consider regarding relying on a Distillation system during an emergency:

  • Smaller units are portable, with some being suitable for use with a fire or camping cooktop
  • However, portable units will not provide sufficient water for multiple individuals
  • A heating source may not be available
  • If a source of fuel is available, the system will require this precious resource
  • Larger units will require electrical power to function, which may not be available

How much do Reverse Osmosis and Distillation systems typically cost?

RO Systems

Reverse Osmosis systems are typically more expensive due to the cost of the system and the additional expense to have the system plumbed. Whole house systems often range from $12,000-$18,000, depending on the amount of water that needs to be generated daily. Under-sink Reverse Osmosis systems typically range from $200-500 plus installation. Overall, cost factors one may consider include:

  • The system
  • Installation
  • Membrane and pre-filter replacements
  • Cleaning and routine maintenance
  • Waste water from the process, which can drive up water bills


Next in cost would be a Distillation unit. Heating water to form steam requires energy (typically electricity, but also potentially a stovetop or fire), which factors into the cost of operating a Distillation unit.

/Small electric, countertop units tend to range from $75-$500. Outdoor, emergency distillers, which look similar to metal pans, are about $100. Cost factors for these types of units are limited:

  • Electricity or another fuel source (wood, propane stove, etc.)
  • Maintenance and cleaning

Larger “automatic” distillers offer higher capacities than countertop units, ranging from about 7-12 gallons per day. They are freestanding units that run from approximately $800-2,500+, depending on the model. Cost factors for larger units include:

  • Installation, if connecting to a tap line
  • Electricity
  • Maintenance and cleaning off scale
  • Filter replacements (many include a carbon filter step)

Note that both Reverse Osmosis and Distillation systems can also be wasteful and inefficient. They use large amounts of water to create a very small amount of purified water, as typically 75-80% of the feed water may end up discarded.15

What are the health concerns associated with Reverse Osmosis or distillation?

Many Reverse Osmosis and distillation systems remove the “good” with the “bad.” Reverse Osmosis or Distillation strips out beneficial minerals from the water, making the water an acidic “hypotonic” solution.16

A chemist will tell you that when a hypotonic (de-mineralized) solution comes into contact with a “hypertonic” (mineralized) solution, the minerals within the hypertonic solution will transfer out of hypertonic solution and into the hypotonic solution until equilibrium is achieved.17 What this simply means is that when one drinks hypotonic water, the minerals in the blood and lymphatic system, which are hypertonic, transfer into the hypotonic Reverse Osmosis or Distilled water that is consumed and the minerals are flushed out of the body upon urination. In an effort to re-mineralize, the blood and lymphatic systems then begin to scavenge for minerals from other parts of the body, such as bones and other organs, and this process repeats itself every time de-mineralized hypotonic water is re-consumed.

Several studies suggest that people who drink demineralized water (hypotonic) over a long period of time tend to be more prone to degenerative diseases such as osteoporosis.18

How do Berkey® Systems compare to Reverse Osmosis and Distillation?

Powerful Purification

Black Berkey® Purification Elements are Unique

Berkey® Water Purification Systems address a broad universe of potential contaminants, including viruses, bacteria, pesticides, pharmaceuticals, heavy metals and even radiologicals while leaving in the healthy minerals your body needs.

  • Addresses pathogenic bacteria without a UV light
  • Removes dead bacteria bodies during the purification process
  • No need to turn off water pressure to the home
  • There are no coils to maintain
  • Addresses chlorine, chlorine byproducts and VOCs (among many other chemicals)
  • Not susceptible to contaminants that may pass through Distillation systems in a gaseous state

Black Berkey® Purification Elements Leave in Beneficial Minerals

Berkey® purification systems leave in the beneficial minerals your body needs. Enjoy powerful purification without sacrificing positive components of your water.

Learn More About Black Berkey® Purification Elements

Explore other articles for additional, in-depth performance information:

Convenient to Maintain

Berkey® systems can be easily cleaned by removing all filter elements and then washing the top and bottom chambers of the system in warm water and dish soap. For users in areas of hard water, calcium scale may build up on the spigot and chambers after prolonged use. To remove, simply soak affected part(s) in vinegar or a 50-50 mix of vinegar and water for about 15 minutes.


A Berkey® system also typically costs less than either Reverse Osmosis or Distillation at about 1.8 cents per gallon. Also, Berkey® systems use all of the water that flows through the purification elements, leaving only the contaminants behind.

  • Enjoy a 6,000 gallon lifespan per pair of Black Berkey® Purification Elements
  • Uses water more efficiently, reducing “waste” water and expense
  • Powered by gravity- no electricity or other fuel cost
  • No professional installation cost
  • Limited maintenance required

Fits Virtually Any Need

Berkey® systems are available in seven different sizes, from a 1 quart system to a 6 gallon system capable of producing up to 26 gallons / hour in an emergency. In addition, larger systems may be expanded to accommodate additional purification elements. This speeds up the process, and reduces wait time. Visit our "Find your Berkey® System" page to determine what might work best for your family or group.

Essential During an Emergency

Berkey® systems are portable, require no electricity or water pressure to operate, and are made for the extreme. Berkey® systems can easily purify ordinary tap water and well water, yet are powerful enough to efficiently purify raw, untreated water from sources such as remote lakes and streams. Berkey® systems used several different independent labs, took multiple samples and performed Extreme Testing for Lead and PFC’s in order to review the effectiveness of our Black Berkey® Purification Elements. Test results for Black Berkey® Purification Elements are readily available to interested customers.

Berkey® Sytem Benefits

Make your choice with confidence, based on detailed, high-quality information.

Berkey® Systems are the top choice for everyone who is considering a gravity-fed system. We hope that demonstrating how to evaluate major performance factors assists you in making a great decision.

Berkey® System Benefits

Powerful- Berkey® purifiers remove a broad universe of contaminants, from toxic chemicals and minerals to pathogenic bacteria and virus, while leaving in the healthy minerals your body needs.

Efficient- Berkey® purifiers are the fastest-producing gravity fed water purification systems on the market, purifying water up to eight times faster than other available systems.

Convenient- The purification elements may be cleaned, eliminating frequent replacements.

Effortless- The design replaces slow and exhausting manual pumps with the natural force of gravity. At the same time the system remains simple to use, making it a breeze; whether in the kitchen or deep in the Rocky Mountains.

Portable- Berkey® purifiers travel easily and function without electricity or water pressure.

Durable- Constructed of highly-polished surgical grade AISI 304 stainless steel, the housing is built to last.

Economical- Two Black Berkey® Purification Elements, which come standard with most systems, average 2 cents per gallon of purified water, and last up to 6,000 gallons, or approximately 5-8 years with typical use.

Proven- Used by individuals, missionaries, and relief organizations worldwide, Berkey® systems have truly stood the test of time.

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(1) Biology Online Dictionary- Osmosis
(2) Puretec- What is Reverse Osmosis?
(3) A Guide to Drinking Water Treatment Technologies for Household Use
(4) Cornell Cooperative Extension, College of Human Ecology- Reverse Osmosis treatment of Drinking Water
(5) A Guide to Drinking Water Treatment Technologies for Household Use
(6) Puretec- What is Reverse Osmosis?
(8) What is Reverse Osmosis?
(9) Cornell Cooperative Extension, College of Human Ecology- Reverse Osmosis treatment of Drinking Water
(10) Distilled water
(11) Drinking Water Treatment: An Overview
(12) Contaminants Removed from Water by Distillation
(13) Drinking Water Treatment: An Overview
(14) Water Distillers
(15) Environmental concerns of desalinating seawater using reverse osmosis.
(16) Dr. Jacqueline Gerhart: There's good and bad to using reverse osmosis water systems
(17) Tonicity
(18) What Are the Dangers of Drinking Distilled Water?