General RO Questions
- How do I determine the flow rate in my home?
- Can an RO System achieve 100% recovery or 100% separation?
- Do RO membranes reject antimony, arsenic, lead, and thallium?
- What is the difference between NF & RO?
- What filter pore size is recommended as pretreatment in a RO system?
- Will Iron Damage an RO Membrane/System?
- Does RO Waste Water Down the Drain?
- What happens to the impurities that are removed from the water?
- Why is the pH of RO permeate lower than the feedwater pH?
- Does RO Remove Parasites, Cysts, Bacteria Or Cryptosporidium?
- Is RO Better than a Faucet or Pitcher Filter?
- What is TDS?
- What is Reverse Osmosis?
- What type of pretreatment does RO need?
- Is RO water too pure for use in my espresso machine?
- What lubricant should I use for the seals in an RO System?
- What contaminants will Reverse Osmosis remove from the water?
- What is the difference between Brackish and Seawater?
- How do I determine the flow rate in my home?
Visit our Flow Rate and Sizing Guide for detailed instructions.
If you need to figure out the flow rate in gallons per minute of a steady flow in to a holding tank, or open discharge: To estimate the flow rate of water into your home:
• Make sure no water is running in the house
• Use the faucet closest to the water source (pump, tank or pipe)
• Open the faucet completely and measure the time it takes to fill a one US gallon container
• Divide 60 seconds by the time it took to fill the container flow rate
• EXAMPLE: If it takes 20 seconds to fill a 1 gallon container, the flow rate is 3 gallons per minute.
[Back To Top] - Can an RO System achieve 100% recovery or 100% separation?
No, 100% separation is not possible with thin film composite membranes. Also, 100% recovery is not possible with thin film composite membranes. With thin film composite membranes, there are always three streams (feed, concentrate, and permeate). As the permeate water is being produced, the feed water is being concentrated, but it can not be separated 100%. Also, since there is always a concentrate stream, 100% recovery is not possible. Percent recovery is defined by permeate flow rate divided by feed flow rate x 100%.
[Back To Top] - Do RO membranes reject antimony, arsenic, lead, and thallium?
Some general guidelines are given below, but need to be verified by pilot testing for each situation. Rejection of lead by thin film RO membranes has been reported to be quite high, >99%.
The rejection of arsenic depends on its oxidation state. The +3 acid, arsenious, is not rejected particularly well in neutral solutions, 70 to 90%, but is well rejected as the pH approaches or exceeds 9.2. The +5 arsenic acid is well rejected in neutral solution.
[Back To Top] - What is the difference between NF & RO?
Nanofiltration is a membrane liquid separation technology that is positioned between reverse osmosis and ultrafiltration. While RO can remove the smallest of solute molecules, in the range of 0.0001 micron in diameter and smaller, nanofiltration (NF) removes molecules in the 0.001 micron range.
NF is a poly piperazine amide membrane and is essentially a lower-pressure version of reverse osmosis where the purity of product water is not as critical as pharmaceutical grade water, for example, or the level of dissolved solids to be removed is less than what is typically encountered in brackish water or seawater. As such, nanofiltration is especially suited to treatment of well water or water from many surface supplies.
Nanofiltration is used where the high salt rejection of reverse osmosis is not necessary, and yet NF is still capable of removing hardness elements such as calcium or magnesium. Sometimes referred to as "membrane softening", nanofiltration is an attractive alternative to lime softening or sodium chloride zeolite softening technologies. And since NF operates on lower pressure than does RO, energy costs are lower than for a comparable RO treatment system.
[Back To Top] - What filter pore size is recommended as pretreatment in a RO system?
Most commonly a filter with a micron-rating of 5 micron absolute. With high levels of colloidal silica, lower micron-ratings are advisable.
[Back To Top] - Will Iron Damage an RO Membrane/System?
Yes. Iron is not effectively flushed from the membrane during the reverse osmosis process, and will build up and clog the membrane. Water containing more than 1ppm of iron should be treated to remove the iron before it reaches the RO system.* Trace amounts of iron (up to 2 ppm) can be removed using a water softener. Greater concentrations of iron require removal by a pyrolox or manganese greensand filter.
[Back To Top] - Does RO Waste Water Down the Drain?
A percentage of the water that enters the system is directed to the drain. This water is flushing away the impurities that are rejected by the reverse osmosis membrane, and that cannot be removed by conventional filtration.
Our Reverse Osmosis systems use an automatic shut-off valve, which shuts off the feed to the system as soon as the tank is full. This prevents water from flowing down the drain when the system is not in use.
[Back To Top] - What happens to the impurities that are removed from the water?
The RO Membrane separates the pure water from the impurities, and the impurities are washed down the drain. Unlike conventional filters, RO membranes are self-cleaning. As the water flows through the membrane, good water is forced through the membrane and into the permeate tube, and the rejection water stream flushes the rejected impurities out of the membrane, to the drain.
[Back To Top] - Why is the pH of RO permeate lower than the feedwater pH?
The pH of water depends on the amount of dissolved carbon dioxide and alkalinity. RO membranes remove alkalinity but not carbon dioxide. The permeate has much lower amount of alkalinity and the same amount of carbon dioxide as feed. This combination of low alkalinity and the same amount of carbon dioxide creates a lower pH in permeate than the feed.
[Back To Top] - Does RO Remove Parasites, Cysts, Bacteria Or Cryptosporidium?
No health claim can be made due to uncontrolled issues such as regular maintenance. However, these items are too large to pass through the thin film RO membrane. NSF has a rating of 1 Micron for reduction of Giardia Cysts and Cryptosporidium is 1 micron. Thin Film Film Reverse Osmosis Membranes filter down to 1/10,000 of a micron.
[Back To Top] - Is RO Better than a Faucet or Pitcher Filter?
Most faucet and pitcher filters on the market use granular activated carbon to remove chlorine, taste and odor from the water. While this will improve the taste of the water, it does not remove any dissolved solids or the majority of contaminants that are removed by the reverse osmosis membrane.
Our reverse osmosis systems incorporate carbon filters as pre and post treatment for the reverse osmosis membrane.
[Back To Top] - What is TDS?
Total Dissolved Solids (TDS) are the total amount of mobile charged ions, including minerals, salts or metals dissolved in a given volume of water, expressed in units of mg per unit volume of water (mg/L), also referred to as parts per million (ppm). TDS is directly related to the purity and quality of water and water purification systems.
"Dissolved solids" refer to any minerals, salts, metals, cations or anions dissolved in water. This includes anything present in water other than the pure water (H20) molecule and suspended solids. (Suspended solids are any particles/substances that are neither dissolved nor settled in the water, such as wood pulp.)
In general, the total dissolved solids concentration is the sum of the cations (positively charged) and anions (negatively charged) ions in the water.
Parts per Million (ppm) is the weight-to-weight ratio of any ion to water.
[Back To Top] - What is Reverse Osmosis?
Reverse osmosis is a membrane separation process in which feed water flows along the membrane surface under pressure. Purified water permeates the membrane and is collected, while the concentrated water, containing dissolved and undissolved material that does not flow through the membrane, is discharged to the drain.
The key requirements of Reverse Osmosis process are a membrane and water under a pressure. Other requirements include prefiltration to remove suspended impurities and carbon to remove chlorine (damages the membrane).
Most membranes remove 90-99+ % of the dissolved impurities depending on the impurity and the composition of water.
Reverse osmosis systems remove salts, microorganisms and many high molecular weight organics. System capacity depends on the water temperature, total dissolved solids in feed water, operating pressure and the overall recovery of the system.
[Back To Top] - What type of pretreatment does RO need?
Typical pretreatment consists of:
- Coarse filtration (~80 micron) to remove large materials - City water has typically been filtered to meet this standard.
- Hypochlorite addition to reduce biofouling potential – City water has typically been treated by chlorine or chloramines for this purpose.
- Fine filtration using multimedia filters or clarification.
- Carbon Filter or Bisulfite addition to reduce remove residual free chlorine.
- Water Softener or Antiscalant to remove hardness and prevent scaling.
- Cartridge 5 Micron Sediment filter upstream of the feed pump and membranes Additional pretreatment considerations: Water with higher particle contents, measured by silt density index (SDI), require a higher degree of pretreatment to achieve acceptable quality. Systems using groundwater as the feed source frequently operate without hypochlorite and bisulfte addition. Waters with high hardness may require softening and/or acid addition. Activated carbon may be needed for water with high organic content.
[Back To Top] - Is RO water too pure for use in my espresso machine?
I am using RO water for our espresso machine. Is it possible that the water may be too pure to allow the electric steam generator level controller to operate successfully?
Pure water will not conduct electricity. For this reason if your steam generator level controller operates by measuring electrical currents, the water may be too pure to allow it to operate successfully. We recommend using a Nanofiltration Element instead of RO, which will remove only 80% of the Ions, compared to 99% by RO.
[Back To Top] - What lubricant should I use for the seals in an RO System?
You will need a special lubricant so as to not damage the membrane in your system. The product part # to search for is H-C111DC.
[Back To Top] - What contaminants will Reverse Osmosis remove from the water?
Ion % Rejection* Calcium 93-99 Sodium 92-98 Magnesium 93-98 Potassium 92-96 Manganese 96-98 Iron 96-98 Aluminum 96-98 Copper 96-99 Nickel 96-99 Cadmium 93-97 Silver 93-96 Zinc 96-98 Mercury 94-97 Hardness Ca&Mg 93-97 Radioactivity 93-97 Chloride 92-98 Ammonium 80-90 Bromide 90-95 Phosphate 95-98 Cyanide 90-97 Sulfate 96-99 Thiosulfate 96-98 Silicate 92-95 Silica 90-98 Nitrate 90-95 Boron 50-70 Borate 30-50 Fluoride 92-95 Polyphosphate 96-98 Orthophosphate 96-98 Chromate 85-95 Bacteria 99+ Lead 95-98 Arsenic 50-90
[Back To Top] - What is the difference between Brackish and Seawater?
Brackish water is water that has more salinity than fresh water, but not as much as seawater. Brackish water is typically 1,000 - 15,000 ppm. Anything above 15,000 ppm and up to approximately 50,000 ppm is considered seawater.
[Back To Top]