Government of Nova Scotia Government of Nova Scotia Nova Scotia, Canada


Drinking Water

Reverse Osmosis to Remove Arsenic from Drinking Water

What is reverse osmosis?

Reverse osmosis removes most impurities from water. Water is forced through a membrane. The contents of the water, including arsenic, are left behind on the membrane while treated water passes through.

Where should the reverse osmosis unit be installed?

Reverse osmosis units can be installed either at the point-of-entry or at the point-of-use. Point-of-entry means that the treatment unit is installed where the water enters the home or building so all water will be treated. Point-of-use means that the treatment unit is installed at the tap so only water used from this tap is treated.

It may be more economical to use reverse osmosis only on the taps that will be used for drinking, cooking and dental hygiene. Water should not be consumed from taps that are not treated by the reverse osmosis unit.

Is the reverse osmosis unit affected by raw water quality?

A reverse osmosis unit may be affected by raw water that is muddy or cloudy, hard, or high in chlorine, iron or manganese. You may need to install additional treatment units prior to the reverse osmosis unit to ensure it operates efficiently and economically. You should consult a reputable water treatment specialist to determine what is required.

How effective is the reverse osmosis unit in removing arsenic?

Reverse osmosis units are capable of removing arsenic. However, pre-treatment may also be required depending on raw water quality characteristics.

How practical or difficult is the reverse osmosis unit to operate and maintain?

The reverse osmosis unit is simple to operate and to maintain. It does not require any chemical addition. Routine maintenance includes replacing the membrane and the filter when required. Like any piece of water treatment equipment, it is important to follow the manufacturer's instructions for maintenance.

How much does a reverse osmosis unit cost?

A typical point-of-use reverse osmosis unit can cost $300 to $1,000 (2005). Larger point-of-entry units for treating an entire home or building may cost $6,000 and up.

How much does it cost to operate and maintain the reverse osmosis unit?

The pre-treatment sediment cartridge should be replaced each year and they cost approximately $45. The actual membrane should last up to five years, depending on the quality of your raw water. A new replacement membrane costs about $100 (2005).

What happens to the substances that are taken from the water and how much wastewater is created by the reverse osmosis unit?

Up to half of the water supplied to an reverse osmosis unit will be wastewater, which is flushed out to the drainage system. In some systems, this reject water can be recycled. Along with the reject water, the contaminants collected by the membrane are flushed out to a drainage system.

Reject water from point-of-use reverse osmosis units may be discharged to a septic system. However, the reject water from larger point-of-entry reverse osmosis units should not be discharged to a septic system unless a professional engineer with expertise in on-site services has confirmed that it is acceptable to do so.

Does the reverse osmosis unit remove other contaminants from water supplies?

The reverse osmosis unit can remove most substances you might expect to find in drinking water including arsenic, chloride and nitrates.

Does reverse osmosis have any side effects or drawbacks?

Water treated with reverse osmosis can be corrosive, however this is generally not a problem for households using the unit as a point-of-use device to treat drinking water.

For some consumers, water treated with reverse osmosis may have a bland taste due to the removal of all minerals. As well, reverse osmosis units remove beneficial minerals such as calcium and magnesium. It is important to consume a reasonably well-balanced diet to offset the removal of these minerals.

Reverse osmosis units do not produce large quantities of water in a short period of time and in some cases units may reject more water than they produce.

Are there any manufacturers that make a better unit?

Nova Scotia Environment does not recommend specific brands of treatment devices, however it is strongly recommended that consumers use devices that have been certified by an accredited certification body as meeting NSF Standard # 58 - Reverse Osmosis Drinking Water Treatment Systems.

Where can I get the reverse osmosis unit?

Units are available from water treatment companies in Nova Scotia. Check the Yellow Pages of your telephone book under the heading Water Treatment for a list of water treatment dealers.