RO systems

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Reverse osmosis (RO) purification involves forcing water through a semi-permeable membrane to remove minerals and other impurities. Water moving across the membrane from high salt concentration to low concentration is the reverse of natural osmosis. To achieve this, pressure must be applied, usually via municipal water pressure or sometimes with a pump. RO is a type of crossflow filtration, having two output streams: one with the purified water and one that carries away the waste. An RO system typically removes at least 90% of the dissolved solids. Usually only around 20% of the feed water is captured as filtered water in a home RO system (i.e. for every 1 gallon collected, 4 gallons go down the drain); this may be a concern in areas there water availability is limited and/or disposal is problematic or expensive.

Terminology:
Permeate - The purified water that passes through the RO membrane.
Concentrate - The waste water that does not pass through the RO membrane. It contains relatively higher amounts of dissolved solids (e.g. salts).
Recovery rate - The percentage of permeate collected from the water entering the system.
Rejection rate - The percentage of dissolved solids removed by the filter.
Total dissolved solids (TDS) - The mineral content of the water, expressed as parts per million (ppm, which is effectively the same as mg/L).

Best RO systems

There's apparently only one system on the market with high-quality components, intelligent design, and a competitive price.

Product	Stages	Features
Buckeye Hydro Premium RO System Editor's pick	Sediment filter, 1 micron, multi-layer Carbon block filter, 0.5 micron, 20,000 gal capacity FilmTec™ RO membrane, 24–100 gpd	Includes: Pressure gauge Clear housings Mounting bracket Tubing Housing wrench Drain saddle Excellent customer service Options: Catalytic carbon stage to remove chloramines Manual or automatic flush valve Automatic shut-off valve In-line TDS meter Choice of feed water adapter Drinking water add-on Many other accessories also available

You could potentially save some money by DIY. It is possible to build a RO system from scratch since many of the vendors that sell RO systems also sell all of the individual parts.

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Potential vendors

• https://spectrapure.com/ (and here - affiliate)
• http://www.premierwatersystems.net/
• https://airwaterice.com/
• https://www.uswatersystems.com/
• https://www.marinedepot.com/aquafx-dolphin-reverse-osmosis-system-100-gpd - affiliate

System components

Filters

A typical RO system treating chlorinated water contains a default configuration of 3 stages:

1. Sediment filter
2. Carbon block filter
3. RO membrane

Sediment pre-filters

These are designed to remove particulates from the water, including bacteria, clay, colloidal silica, and iron corrosion products (rust). Removal of sediment prolongs the life of other filters, and therefore it should always be the first stage of filtration. Sediment filters come in a variety of pore sizes rated in microns. The smaller the pore size, the more effective they are at removing particulates. Pore size of 5 micron or smaller is recommended. Smaller pores such as 1–3 micron will help prevent silica fouling of the RO membrane. Filters having multiple layers with different pore sizes are most efficient and have a longer life. The pore size on the sediment filter should be about equal to, or smaller than the carbon block pore size.

Summary of the ideal sediment filter:

• Pore size no larger than 5 microns
• Pore size about the same as the carbon block(s) or smaller
• Positioned as the first stage in the RO system

Carbon pre-filters

Activated carbon removes many unwanted compounds from the water, but most importantly it removes the chlorine that would otherwise harm the RO membrane. Three forms of activated carbon filters are seen in water filtration systems: granulated activated carbon (GAC), carbon block, and catalytic carbon.

GAC should be avoided as a pre-filter. A carbon block will typically offer much better performance at only very marginally increased cost.

Every RO system should contain a carbon block. Pore size typically ranges from 0.5 to 10 microns. Smaller pores remove chlorine and other compounds more effectively and provide greater protection to the RO membrane. Carbon blocks are also rated by the volume of water that can pass through before they need to be replaced. This can range from a few hundred gallons up to 20,000 gallons. Only ONE carbon block is needed. Many RO systems on the market contain multiple low-quality carbon blocks; these systems intend to trick you into thinking more stages is better and they are designed to sell you more replacement filters. Using just one high-quality carbon block will improve performance, reduce cost, and reduce system maintenance required. Note: carbon blocks are not very effective at removing chloramine.

Catalytic carbon is an advanced activated-carbon product designed to remove chloramines. Catalytic carbons may also remove hydrogen sulfide gas, which produces the "rotten egg" smell in some well water. If there is chloramine in your water, a catalytic carbon filter stage should definitely be used because chloramines will damage the RO membrane.

Summary of the ideal carbon pre-filter:

• Positioned between the sediment filter and RO membrane
• Carbon block, not GAC
• Smaller pore size is best, 0.5 or 1 micron
• Higher volume rating is best
• Use only one carbon pre-filter with the following exception
• A catalytic carbon stage is needed if your water has chloramines

RO membrane

The RO membrane removes dissolved minerals and other contaminants from the water. There are two types of RO membranes: thin film composite (TFC) and cellulose triacetate (CTA). TFC is preferred because it has a higher rejection rate and longer lifespan. FilmTec™ membranes for example are among the most reliable and consistent TFC elements in the industry. Be wary when purchasing a system if it doesn't specify what type of membrane is included.

Home RO membranes have different production flow (flux) ratings that indicate how quickly purified water is produced, typically ranging from 24 to 100 gallons per day (gpd). Lower flux membranes have a higher rejection rate, and the lower flow rate also improves the effectiveness of the carbon filters due to longer contact time. For these reasons, it's best to choose the lowest flux membrane that can keep up with demand. Be aware that the actual performance of your system won't exactly match the manufacturer flux rating because your system will have different operating conditions from factory specification.

Summary of the ideal RO membrane:

• FilmTec™ or other TFC membrane
• Lower flux is preferred (i.e. 24-50 gpd)

Deionization (DI) stage

A DI stage can be used to remove any remaining minerals that the RO membrane failed to reject. These systems are often called "RODI". Very few people use this for brewing water because it's not worth the added expense and maintenance — the low amount of minerals remaining in water from a functional RO system will have no significant impact on the brewing process.^{[citation needed]}

Carbon post-filter

An extra carbon filter after the RO stage can possibly be helpful to improve the taste of the water, and therefore might be something to consider if you will be using the water for drinking. GAC is typically preferred as a post-filter because it's generally beneficial to minimize resistance on the permeate stream, and high performance isn't needed at this stage.

Filter housings

There are two different types of filter housings on home RO systems:

1. Standard housings
2. Single-use housings (sometimes called inline filters)

Standard housings (e.g. Buckeye Hydro Premium system) are designed to hold standard-sized filters (2.5" x 10"), which means that you can shop anywhere for replacement filters and you have many different options. Standard housings may be clear or opaque.

Single-use housings (e.g. APEC Countertop system - Amazon) are designed for convenience, but you will typically pay a much higher price for replacement filters and have fewer options for replacement filter product specifications. Keep in mind that even with these disposable housings, the system still needs to be cleaned periodically.

Pressure gauge

A pressure gauge can be used to read the water pressure in the system after the pre-filters and before the RO membrane (any other positioning is inappropriate). This provides some very useful information:

• It will tell you whether your home's water pressure is sufficient.
• Decreasing pressure indicates that one or more of the pre-filters are clogged and need to be replaced. (see maintenance below)
• Increasing pressure may indicate excessive microbial growth on the RO membrane (biofouling).

TDS meter

A Total Dissolved Solids meter (which actually measures water conductivity and merely estimates TDS) is an essential tool for monitoring RO membrane performance. Some systems offer inline TDS monitoring for convenience, but using a handheld meter is perfectly fine. See TDS testing for meter recommendations; they are inexpensive and very easy to use.

Flush valve

A flush valve temporarily allows a higher flow of water through the system to flush minerals and organic contaminants (including microbes) away from the RO membrane. Periodic flushing is important for proper system maintenance and longevity of the RO membrane (see the maintenance section below). Therefore a flush valve is highly recommended, either manual or automatic.

As the name implies, a manual flush valve must be opened and closed by hand whenever you need to flush the system. It's easy—just turn the valve 90°, but you need to remember to do it.

An automatic flush control system fully automates the flushing process. Depending on the product, it can flush the membrane for a short period at start-up, every hour during operation, and at shut-down. Keep in mind this device requires power to operate, unless the rest of a basic RO system.

• Buckeye Hydro flush kits

Pumps

There are two different kinds of pumps that may be used in an RO system, each for a different purpose:

1. Booster pump - for low line pressure
2. Permeate pump - for pressurized storage tanks

If your water line pressure is too low for the system to operate efficiently (i.e. under 40psi), then a "booster pump" can be used to increase the water pressure on the RO membrane. It should be added between the carbon block and the RO membrane, rather than before the entire system.

If you are using a pressurized storage tank, a permeate pump is highly recommended. This device helps pump the permeate into the tank and will dramatically improve system performance. It does not require electricity to operate since it utilizes the hydraulic power from the waste water.

Collection accessories and storage tanks

There are 3 basic water collection options for brewers:

1. Open vessel
2. Open vessel with float valve
3. Pressurized storage tank

Collection in an open (unpressurized) vessel simply requires placing the end of the permeate tubing into whatever vessel you want to fill with water. You will need to manually turn off water flow to the RO system when the vessel is full. The obvious major downside to this method is that the vessel will overflow if it runs for too long. A simple solution to avoid problems in that case is to place the collection vessel in a sink, in a tub, on the ground near a drain, or outside if conditions allow.

If you don't want to babysit the system while it is running, you can use a dedicated vessel with a float valve installed. The float valve will shut off the permeate flow when the water fills to the level set by the valve (similar to how a toilet tank works). In this setup, an automatic shut off valve (ASOV) is also needed to shut off the flow of water from the local water supply line. Otherwise waste water would continue to flow down the drain after filling stops. Additionally, a check valve is needed to prevent backflow through the RO membrane. Keep in mind that tanks and plumbing in contact with the filtered water should be plastic (or lined with plastic) because the purified water is corrosive to metal. If metal must be used for the collection vessel, stainless steel is preferred.

The third option is to store the water in a pressurized storage tank, which is designed to dispense water on demand and refill automatically. The tank contains an air bladder to increase pressure as the tank fills with water. Driven by this pressure, the tank can dispense water to a dedicated faucet, or even plumbed directly into an automated brewing system. Be aware that the actual capacity of a tank is less than what the manufacturer indicates because of the air bladder. For example, a 4.5 gallon tank will actually hold around 2.5-3 gallons of water. Furthermore, the exact amount of water the tank is capable of holding will differ based on the feed pressure and the settings on the shutoff valve. A 14 gallon pressure tank is appropriate if you want to store 6 to 8 gallons of RO water. As mentioned above, a permeate pump is highly recommended because the back-pressure from the pressurized tank will significantly deteriorate every aspect of system performance: decreased rejection rate, decreased recovery rate, slower production speed.

Installation

Here we have a few tips for installation.

Connecting to the source water

• The easiest way to feed water into the system is to connect it to a garden hose spigot (bibb) in your home (e.g. in a utility sink or laundry area) or even outside temporarily.
• A similar option is to use a faucet adapter to connect it to a sink faucet, although be aware that many modern sink faucets will not accept common adapters.
• Another relatively easy option is to use an adapter to connect to the under-sink shut-off valve.
• Lastly, the system can be attached directly to a water line in your home if you have some plumbing knowledge.

Softened water

If you have a water softener, it's best to install the RO system after the softener. In other words, feed the softened water into the RO system. This improves the RO system performance.

Drainage

The waste water needs somewhere to drain. One option is to simply place the waste water tubing in a sink or any other drain. Be careful that the tubing doesn't move away when the pressure changes stirring flushing.

A more permanent solution is to use the drain saddle that comes with pretty much every RO system. This simple device secures the waste tubing to a drain pipe below a sink, in which you have drilled a 1/4" hole. Don't worry; the vertical sink pipe is fairly simple to replace later if needed.

Initial setup process

First time setup generally consists of:

1. Make sure all the tubing is attached correctly.
2. Flush the carbon filter(s) for 10 minutes.
   • The RO membrane should not yet be installed during this step.
   • It is normal for carbon filters (especially GAC) to release some black grit during the first flush.
3. Check for leaks.
4. Install the RO membrane.
5. Allow the system to run for about 90 minutes or produce 3 gallons of permeate, whichever takes longer.
   • To remove any air bubbles, hold the RO membrane housing vertically with the outflow upward for around 10-15 seconds.
   • The initial water must be discarded.
6. Check again for leaks.

Optimization

Optimizing your system can potentially lead to better purification, less waste water, and faster production speed. The first step is to measure system performance.

There are 3 useful metrics:

1. Pressure on the RO membrane
2. Rejection rate
3. Recovery rate

Pressure

Measuring the pressure requires a pressure gauge. A gauge can be added if your system doesn't have one included.

• Pressure gauge from Buckeye Hydro

RO systems operate best with at least 40-50 psi. With increasing effective feed pressure, the permeate TDS will decrease while the recovery rate will increase. Around 80 psi is a reasonable maximum and will provide exceptional performance.

If your line (plumbing) pressure exceeds 80 psi, you should install a pressure regulator to reduce the pressure. Conversely, if you need to increase your line pressure, install a booster pump between the pre-filters and RO membrane.

• Pressure regulator from Buckeye Hydro
• Aquatec 8800 booster pump from Buckeye Hydro

Rejection and recovery rates

Rejection rate is easy to measure. Test the TDS of the source water and the permeate under normal usage conditions. If the rejection rate isn't at least 90-95%, you should perhaps try to re-seat the RO membrane to make sure it isn't leaking; consider also using a food-grade lubricant on the seals.
Rejection rate = 1 – (Permeate TDS ÷ Source TDS)

Measuring recovery rate is a little more involved. A simple way to measure the output volumes is to line up 6 to 8 identical cups (e.g. Solo cups) in front of your RO system outputs. You may use more precise measuring equipment if you have it available. Make sure the automatic flush system is turned off during the test if your system has one.

• Systems without a pressurized tank: With your concentrate tube in one hand, and your permeate tube in the other, determine how many cups are filled with concentrate in the time it takes to fill one with permeate.
• Systems with a pressurized tank: Measure the concentrate output in the cups starting from when you begin dispensing one cup of permeate from the tank. Measure the waste water until it is done flowing (i.e. until the tank has been refilled).

The RO membrane cartridge has a small outflow orifice (flow restrictor) to limit the waste flow and create a high pressure on the membrane. If more than 4 cups of concentrate are produced for one cup of permeate, then a tighter flow restrictor would be beneficial. The flow restrictor is inexpensive and easy to replace in most systems. For systems with pressurized tanks, a permeate pump would greatly improve the recovery rate.

• Aquatec permeate pump

Other factors like water temperature and source water TDS can also affect performance, but aren't easy to control. For example, water temperature is one of the most important factors affecting performance. Colder water and/or lower water pressure will result in slower production and lower recovery rate. Buckeye Hydro has a calculator to help predict the effects of various water temperature and pressure. If your source water has very high TDS, a water softener may be something to consider.

Maintenance

Regular maintenance will extend the life of your system and ensure that it continues to produce high quality water.

Replacing filters

Replacing pre-filters regularly is necessary to protect the more expensive RO membrane. Fortunately, filter and housing sizes are standardized. Nearly all residential RO systems are designed to utilize 2.5 inch diameter x 10 inch length filters.

Sediment filters should generally be replaced every 6 months, or according to the product specifications. However, the actual lifespan varies depending on the source water quality and how often the system is being used. If you would rather be more precise about when to replace it, use a pressure gauge after the pre-filters. When the pressure begins to decrease, it's time to replace the pre-filters. If your system has a pump before the RO membrane, it needs to be turned off to appropriately measure the pressure.

For best results, the carbon block should be replaced after it has filtered 50% of the stated capacity. Manufacturers recommend flushing new carbon block cartridges for at least 10 minutes before using the product water. Don’t run flush water through other stages in your system. This is especially important if you are using catalytic granular activated carbon (CGAC) to treat chloramines.

The RO membrane is the most expensive part of the system. It must be replaced when the rejection rate begins to decrease, which usually corresponds to an increased TDS. For monitoring, a TDS meter should be used to compare the permeate TDA to the source water TDS. Allow the system to run for a few minutes before checking. If you have a pressure tank, the TDS of the permeate needs to be measured with the pressure tank valve closed. Membranes commonly produce purified water more slowly as their function declines. Also be aware that the TDS of the permeate tells you nothing about the condition of your pre-filters or when to change them. If the system is well-maintained and the pre-filters are consistently replaced on time, the RO membrane should last several years. See TDS testing. Manufacturers recommend flushing new RO membranes for up to 40 minutes to remove preservatives before using the product water. Don’t run flush water through other stages in your system. (Dupont suggests 60 minute flush for FilmTec™ membranes.)

If your system has a DI resin, it often has a visual color-change indicator to help determine when it needs to be replaced. However, the color indicator is not particularly accurate, so it is highly recommended to monitor TDS before and after the DI resin as well as the source water. A poorly functioning RO membrane will quickly expend the DI resin.

In summary, two tools are required for proper filter monitoring:

1. A pressure gauge after the pre-filters
2. A TDS meter

Usage frequency

RO membrane manufacturers recommend that the system be used at least once a week to avoid biofouling from microbe growth in stagnant dechlorinated water.

When the membrane system is shut down, the system must be flushed until concentrate TDS matches feedwater TDS.

When the high-pressure pump is switched off, and the feed/concentrate side had not been flushed out with permeate water, a temporary permeate reverse flow will occur by natural osmosis. This reverse flow is sometimes referred to as permeate draw-back or suck-back. Permeate suck-back alone or in combination with a feed-side flush may provide a beneficial cleaning effect. To accommodate permeate suck-back, enough water volume should be available to prevent a vacuum from being drawn or air being sucked back into the membrane element.

When the system must be shut down for longer than 48 hours, take care that:

• The elements do not dry out. Dry elements will irreversibly lose flux.
• The system is adequately protected against microbiological growth, or regular flushing is carried out every 24 hours.
• When applicable, the system is protected against temperature extremes.

Cleaning

The carbon block removes the chlorine that protects the water from microbial growth. Therefore the RO membrane, cartridges, and purified water and anything else downstream from (and including) the carbon filter are all susceptible to accumulating microbes. As such, periodic cleaning of the system is recommended, along with regular use to avoid stagnant water. Additionally a final pass through a sterile filter or UV light sterilizer may be used if the water needs to be sterile (which is generally not necessary for brewing).

Sanitize the entire system at least once per year, and wash and lubricate the housing o-rings with food-grade silicone grease every filter change.

Scaling is controlled by preventive membrane cleaning. This allows the system to run without softening or dosage of chemicals. The simplest way of cleaning is a forward flush at low pressure by opening the concentrate valve. Short cleaning intervals are more effective than long cleaning times (e.g., 30 seconds every 30 minutes).

Because of the risk of membrane oxidation, chlorine is not recommended for intentionally sanitizing membrane systems. Other oxidizing agents such as iodine, chlorine dioxide, hydrogen peroxide, ozone, and permanganate are capable of damaging RO membranes also if not used properly.

Sodium bisulfite can be added into the feed stream (for a limited time period) during normal plant operation. This intermittent application is often referred to as shock treatment. In a typical application, 500 – 1,000 mg/L NaHSO3 is dosed for 30 minutes. Use only sodium metabisulfite (food-grade) that is free of impurities and not cobalt-activated. The treatment can be carried out on every 24 hours or only when biogrowth is suspected. The efficiency of such treatment should be studied. The permeate produced during dosage will contain some bisulfite, depending on the feed concentration, the membrane type and the operating conditions. Depending on the permeate quality requirements, the permeate can be used or discarded during shock treatment. Bisulfite is effective against aerobic bacteria but not against anaerobic microorganisms.

The best option for cleaning is a two-stage approach:

1. NaOH 0.1% soak (e.g. overnight). Flush afterward with RO permeate.
2. Citric acid 2% soak. Flush afterward with RO permeate.

See Cleaning for further explanation of this approach.

FilmTec™ Elements can operate over a pH range of 2–11, are resistant to compaction and are suitable for temperatures up to 45°C.

Sanitizing

After cleaning, sanitizing may be performed.

Circulate a solution of 0.2% hydrogen peroxide diluted with RO permeate at a temperature below 77°F (25°C) for 20 minutes.  A pH of 3–4 gives optimal biocidal results and longer membrane lifetime. Following these instructions is important to prevent membrane damage.

Sulfite + acid may be another option to sanitize.

Some sources suggest using a 30-minute soak in bleach to sanitize.

Storage

Preservation and Storage Any FilmTec™ Element that has been used and removed from the pressure vessel for storage or shipping must be preserved in a preservation solution as follows:

• Use the standard storage solution of 1% food-grade SMBS (not cobalt-activated) in good-quality water (preferably reverse osmosis (RO) or nanofiltration (NF) permeate).
• Soak the element for 1 h in the solution; keep it in a vertical position so that the entrapped air can escape. Allow it to drip out, and seal it into an oxygen barrier plastic bag. We recommend reusing the original bag or original spare bags available from DuPont. Do not fill the plastic bag with the preservation solution—the moisture in the element is sufficient, and leaking bags might create a problem during transport.
• Identify the element and the preservation solution on the outside of the bag.
• The temperature should not exceed 95°F (35°C) or drop below freezing.
• Re-preserved elements should be visually inspected for biological growth every three months. If the preservation solution appears to be not clear the element should be re-preserved and repacked as above. 
• The pH of the preservation solution must never drop below pH 3.  In the absence of a buffer such as is used in the original preservative for wet FilmTec™ Elements, a pH decrease can occur when bisulfite is oxidized to sulfuric acid. Therefore, the pH of the bisulfite preservation solution should be spot checked at least every 3 months. Re-preservation is mandatory when the pH is 3 or lower.
• Wear protective gloves and sleeves to avoid prolonged contact with skin and sleeves when working with preservative.

Depending on the previous operational history of the plant, it will be necessary in almost all cases to clean the membranes prior to shut-down and preservation. This applies to cases when the membranes are known or assumed to be fouled. After cleaning, the preservation should follow within the next 10 h as follows:

1. Totally immerse the elements in the pressure vessels in a solution of 1 – 1.5% SMBS, venting the air outside of the pressure vessels. Use the overflow technique: circulate the SMBS solution in such a way that the remaining air in the system is minimized after the recirculation is completed. After the pressure vessel is filled, the SMBS solution should be allowed to overflow through an opening located higher than the upper end of the highest pressure vessel being filled.
2. Separate the preservation solution from the air outside by closing all valves. Any contact with oxygen will oxidize the SMBS.
3. Check the pH once a week. When the pH becomes 3 or lower, change the preservation solution.
4. Change the preservation solution at least once a month.

During the shut-down period, the plant must be kept frost-free, and the temperature must not exceed 113°F (45°C). A low temperature is desirable.

See also

• Water
• TDS testing

External links:

• Buckeye Hydro FAQ covers commonly asked questions

• adjusting house water pressure
• more house water pressure info
• chlorine test strips
• https://healthykitchen101.com/best-reverse-osmosis-system-reviews/
• https://www.lenntech.com/Data-sheets/Dow-Filmtec-TW30-1812-75.pdf

Photos

• https://www.homebrewtalk.com/threads/setting-up-ro-water.667227/
• https://www.homebrewtalk.com/threads/my-ro-system.666033/