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


Drinking Water

Anion Exchange to Remove Arsenic from Drinking Water

What is anion exchange?

With anion exchange, water passes through a resin bed which removes arsenic by exchanging it for a non-toxic substance attached to the bed. Once the space on the resin bed is full, the system backwashes with brine to regenerate the bed.

Where should the anion exchange unit be installed?

Anion exchange units are generally installed at the point-of-entry - where the water enters the home or building.

Is the anion exchange unit affected by raw water quality?

Anion exchange units do not specifically target arsenic. Other substances in the water can compete with arsenic for a spot on the resin bed, reducing the effectiveness of the unit. Therefore it is important that the source water be analyzed for other substances that may compete with arsenic. You should consult a water treatment specialist to determine if additional treatment will be required.

How effective is the anion exchange unit in removing arsenic?

Anion exchange 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 anion exchange unit to operate and maintain?

The anion exchange unit is simple to operate and fairly inexpensive to maintain. The resin bed requires cleaning at a frequency that depends on the manufacturer. The resin will require replacement at a frequency dependant on the manufacturer, the quality of the resin, and the quality of the source water. The salt used to make the brine which regenerates the resin bed must be routinely restocked.

If the anion exchange is not properly maintained, the arsenic contained on the resin bed may rapidly detach, leading to higher levels of arsenic in the treated water than the raw water. Therefore, it is important to follow the manufacturer's instructions for maintenance.

How much does an anion exchange unit cost?

A unit large enough to treat drinking water for a household costs in the area of $2,000 to $3,000 (2005).

How much does it cost to operate and maintain an anion exchange unit?

The cost to replace the salt and electricity are the routine operating costs. There will be the cost to replace the resin bed on a less frequent basis. The costs associated with this will be dependent on the unit's manufacturer.

What happens to the substances that are taken from the water?

Arsenic and other substances removed from the water remain on the resin bed until it is backwashed. At that time they are flushed to a drainage system.

Backwash water from the anion exchange unit 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 anion exchange unit remove other contaminants from water supplies?

The anion exchange unit will remove other substances such as nitrate and sulphate from your drinking water.

Does anion exchange have any side effects or drawbacks?

Water treated by the unit may be corrosive because of the low pH and high chloride concentration.

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 # 53 - Drinking Water Treatment Units - Health Effects.

Where can I get an anion exchange 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.