In the preamble of the Department of Health of South Africa (2006) regulations that can be viewed at www.doh.gov.za/department/dir_foodcontr.html are the following definitions for “prepared water”

“prepared water” means bottled water that has undergone any treatment acceptable for bottled waters and may originate from any type of water supply, e.g. distilled tap water, tap water with added minerals”
Dept of Health of South Africa. 2006. Regulations relating to all bottled waters. Foodstuffs, Cosmetics and Disinfectants Act, 1972 (Act no. 54 of 1972) No. R. 718. 28 July 2006

Fundamentally, all water packed into sealed containers and sold for human consumption that does not contain sugars, flavourings (etc) are classified as bottled water. This includes carbonated, natural, mineral, spring and prepared water. Let us examine the prepared waters in more detail. Prepared water is defined as bottled water that has undergone treatment(s) acceptable for bottled waters and may originate from any type of water supply such as environmental sources and municipal sources.

How can prepared water be processed? Legally, prepared waters may be subjected to any anti-microbial treatment and any treatments that modify the physicochemical characteristics of the original water as long as the end result comply with all the legal provisions for all bottled waters.

The labelling of prepared waters must state that it is prepared water, the treatment methods declared as well as the phrase “from a public or private distribution system” if the water was indeed supplied by such a source. This legislation is very much in line with overseas thinking, such as in Canada. Keep in mind that prepared water can originate from any source or combination of sources, such as springs, wells, reservoirs, icebergs, glaciers, rivers and lakes. The difference between prepared water and natural water is solely that prepared water can be treated and modified by various means. All these treated waters are grouped in one category. Natural water must be potable at source whereas prepared water is treated to ensure its potability.

Due to the various sources of prepared water, quality regulations include the absence of heavy metals and classified toxic compounds such as mercury, cyanide and pesticides. But then again, these requirements also pertain to natural mineral water.

Which processes are traditionally used in prepared waters for its purification?

Distillation can be used to purify water. However, distillation is expensive as water needs to be boiled and then condensed, collected and stored. It is noteworthy that chemicals such as some pesticides with a low boiling point will be distilled into the distilled water. Distilled water can also be very acidic (low pH). Distilled water is often called “hungry” water because of the lack of mineral content. It lacks oxygen and minerals and has a flat taste, which is why it is mostly limited to industrial use. I believe that drinking distilled water is unhealthy as it may lead to mineral depletion of your body.

In ion exchange systems, water percolates through bead-like spherical resin materials (ion-exchange resins). Ions in the water are exchanged for other ions fixed to beads. The two most common ion-exchange methods are softening and deionisation. Softening is used primarily as a pretreatment method to reduce water hardness prior to reverse osmosis (RO) processing. The softeners contain beads that exchange two sodium ions for every calcium or magnesium ion removed from the "softened" water. Deionisation beads exchange either hydrogen ions for cations or hydroxyl ions for anions. The cation exchange resins exchange a hydrogen ion for any cations they encounter (e.g., Na+, Ca++, Al+++). Similarly, the anion exchange resins exchange a hydroxyl ion for any anions (e.g., Cl-). The hydrogen ion from the cation exchanger unites with the hydroxyl ion of the anion exchanger to form pure water. The resin must be "regenerated" once it has exchanged all its hydrogen and/or hydroxyl ions for charged contaminants in the water. This regeneration reverses the purification process, replacing the contaminants bound to the resins with hydrogen and hydroxyl ions.

Deionisation can be an important component of a total water purification system when used in combination with other methods such as RO, filtration and carbon adsorption. Deionisation systems effectively remove ions, but they do not effectively remove most organics or micro- organisms. Micro-organisms unfortunately can attach to the resins, providing a culture media for rapid bacterial growth and subsequent contamination.

Carbon adsorption (or carbon filtration) is a widely used method of home water treatment because of its ability to improve water by removing disagreeable tastes and odors, including chlorine. Activated carbon effectively removes many chemicals and gases, and in some cases it can be effective against microorganisms. However, generally, it will not affect total dissolved solids, hardness, or heavy metals. Only a few carbon filter systems have been certified for the removal of lead, asbestos, cysts, and coliform organisms. Activated carbon is created from a variety of carbon-based materials in a high-temperature process that creates a matrix of millions of microscopic pores and crevices. Half a kilogram of activated carbon may provide between 24 and 60 hectares of surface area! The pores trap microscopic particles and large organic molecules, while the activated surface areas cling to, or adsorb, small organic molecules. Carbon also removes free chlorine and protects other purification media in the system that may be sensitive to an oxidant such as chlorine. Carbon is usually used in combination with other treatment processes. The placement of carbon in relation to other components is an important consideration in the design of a water purification system.

Filtration is not unique to processed water as filtration is widely used in the natural water bottling processes. However, filter systems for processed water may also contain stages and types of cartridges that remove certain mineral elements, e.g. nanofilters, ultra filtration, desalination filtration, charcoal filtration and more. Depth filters are usually used as prefilters as they can economically remove up to 98% of suspended solids. Next in line are the surface filters that can remove 99,99% of suspended solids. Lastly, microfilters are used to remove traces of particles and microbes. The above microporous filters remove particles according to pore size. By contrast, an ultrafiltration membrane functions as a molecular sieve, separating dissolved molecules on the basis of size. Ultrafilters remove most particles, pyrogens (dead bacteria), and produces the highest quality water for the least amount of energy.

Many large processors use reverse osmosis membranes to remove salts, chlorine and impurities. They then add a standardised mineral salt solution to the RO water (re-mineralise). They can therefore manipulate and control the taste of the prepared water very closely. Quality is closely monitored and only high purity salts should be used. The consumer can then expect a standardised, specific taste at all times. RO is the most economical method of removing 90-99% of all contaminants. The pore structure of RO membranes is much tighter than the ultrafiltration membranes, and can remove particles, bacteria, pyrogens and organics greater than 300daltons molecular weight. RO is highly effective in removing several impurities from water such as total dissolved solids (TDS), turbidity, asbestos, radioactive isotopes, lead, heavy metals and dissolved organics (e.g. pesticides).

Ozonation can be successfully used to oxidize metal salts such as iron and manganese and to precipitate them. After precipitation, the water must be filtered to ensure the removal of these salts. These specific precipitates are dark coloured, typically rusty colour. Ozonation is mostly used for disinfection purposes. Residues of ozone in bottled water leave a metallic taste. However, this taste will dissipate after a few days in storage as ozone is unstable.

Pasteurisation may be used to remove vegetative micro-organisms from water. Pasteurisation will not sterilize the water, and spore formers such as Bacillus, if present, may multiply after bottling and form floaters. Pasteurisation will be effective against the majority of pathogens. UV radiation is another means of disinfecting clear water. A UV lamp that generates both 185 nm and 254 nm wavelengths will be able to decrease the total organic carbon (TOC) levels to 5ppb through photo-oxidation.

Because each purification technology removes a specific type of contaminant, a well designed water purification system uses a combination of technologies to achieve a specific water quality.

Labelling
The following is required to be indicated on the label:

The name of the product: “prepared water”
The disinfection or treatment method used
The analytical composition in milligrams per litre in the same order as provided in the regulation.
Descriptors as “still” or “non-carbonated” and “sparkling” or “carbonated”
The phrase “from a public or private distribution system” if the prepared water was supplied by a public or private tap-water distribution system.