The heart of a reverse osmosis system is a semi-permeable membrane with very fine pores. Water is forced through this membrane, and any particles or impurities that are too big to fit through the pores are flushed away. The pores are approximately 0.0005 microns in size - for comparison, bacteria range from 0.2 to 1 micron and viruses are 0.02 to 0.4 microns. A typical human hair is about 100 microns wide.

As their name suggests, these filters are filled with a media composed of activated carbon. Particulates are trapped in the small spaces and channels within the media and the activated carbon absorbs many organic molecules. Activated carbon filters therefore provide some protection against sediment in water and a large degree of protection against unwanted colours and odours.

Activated carbon filters can normally be expected to operate for three to five years before the filter media must be replaced.

Greensand filters are designed primarily for the removal of iron from water supplies but they can also be effective in dealing with sulphur problems. Water flowing through such a filter is exposed to greensand media which iron and sulphur are oxidized. The oxidized forms of iron and sulphur are not water soluble. They therefore drop out of solution and collect on the filter media. Periodically, the greensand filter is flushed with a solution of potassium permanganate. This regenerates the media and washes the collected iron and sulphur down the drain.

Down well injection systems are used to provide on-going control of the conditions within a well. Usually used to deliver hydrogen peroxide, down well injection systems are good at controlling biofouling by nuisance bacteria and are also effective against sulphur and methane.

Chlorination systems normally consist of a tank of chlorine which is added to a water supply by a chemical pump. This addition can occur either at a reservoir or in-line, depending on the details of the water system in question. The chemical pump is usually linked to a flowmeter so that the amount of chlorine that is added depends on the amount of water that is used.

Chlorination can be used either to kill bacteria as a means of primary disinfection or to act as secondary disinfection to prevent re-contamination of water which has been cleared of bacteria by, for example, a UV system.

Well pumps are not normally considered to be water treatment equipment but they can have a great impact on both the quantity and quality of the water that is delivered from a well. While it seems obvious that an undersized pump will not deliver the desired amount of water at the desired pressure, it is less widely realized that an undersized pump may leave a "dead zone" in the lower portion of a well which can act as a harbour for bacteria. MacLellan Water Technology is able to specify the right pump for any pumping situation, including constant pressure pumping systems.

Low yield well systems allow wells that produce less than 5 gpm (19 L/min) to be used for regular residential purposes. Low yield well systems require the installation of a storage vessel, a second pump to pump from the storage vessel to the house, and pump controls to regulate water levels.

Bacteria which are found in wells can be divided into two broad classes: disease causing bacteria, of which E. Coli is the most famous example, and nuisance bacteria, which are responsible primarily for aesthetic problems.

Bacteria which are found in wells can be divided into two broad classes: disease causing bacteria - of which Escherichia coli (usually known as E. Coli) is the most famous example - and nuisance bacteria, which are responsible primarily for aesthetic problems.