Purified Water is Water that has been mechanically filtered or processed to remove impurities and make it suitable for use in several commercial and residential applications. Distilled water has been a common form of purified Water but Water is more frequently purified by other processes including deionization, reverse osmosis, carbon filtration, microfiltration, ultrafiltration, UV Oxidation, and EDI.
Combinations of a number of these processes have come into use to produce water of such high purity that its trace contaminants are measured in parts per billion (ppb) ot parts per trillion (ppt) purified water has many uses, largely in the production of medications in science and engineering laboratories and industries, and is produced in a range of purities. It can be produced on site for immediate use or purchased in containers. Purified Water in colloquial English can also refer to water which has been treated to neutralize but not necessarily remove contaminants considered harmful to humans or animals.
Deionized water is a type of purified water with mineral ions (salts) removed. These mineral ions include sodium, calcium, iron, chloride, and bromide. Deionized water is created by taking conventional water and exposing it to electricilly charged resins that attract and bind to salts, removing them from water. Because most of the impurities in water are mineral salts, deionized water is mostly pure, but it does still contain numerous bacteria and viruses, which have no charge and therefore are not attracted to the electrified resins.
Granular Activated Carbon (GAC) is commonly used for removing organic constituents and residual disinfectants in water supplies. This not only improves taste and minimizes health hazards; it protects other water treatment units such as reverse osmosis membranes and ion exchange resins from possible damage due to oxidation or organic fouling. Activated carbon is a favored water treatment technique because of its multifunctional nature and the fact that it adds nothing detrimental to the treated water.
Most activated carbon is made from raw materials such as coconut and coal. Typical surface area for activated carbon is approx. 1,000 square meters per gram. However, different raw materials produce different types of activated carbon varying in hardness, density, pore and particle sizes, surface areas, extractables, ash, and pH. These differences in properties make certain carbons preferable over others in different applications.
The two principle mechanisms by which activated carbon removes contaminants from water are absorption and catalytic reduction. Organics are removed by adsorption and residual disinfectants are removed by catalytic reduction.
Total Dissolved Solids (TDS) is a measure of the combined content of all inorganic and organic substances contained in a liquid in molecular, ionized or micro-granular (colloidalsol) suspended form. Generally the operational definition is that the solids must be small enough to survive filtration through a filter with two-micrometer (nominal size or smaller) pores. TDS are normally discussed only for fresh water systems, as salinity includes some of the ions constituting the definition of TDS. The principle application of TDS is the study of water quality for streams, rivers, lakes, although TDS is not generally considered a primary pollutant it is used as an indication of aesthetic characteristics of drinking water and as an aggregate indicator of the presence of a broad array of chemical contaminants.
Primary sources for TDS in receiving waters are agricultural and residential runoff, clay rich mountain waters, leaching of soil contamination and point source water pollution discharge from industrial or sewage treatment plants. The most common chemical constituents are calcium, phosphates, nitrates, sodium, potassium, and Chloride, which are found in nutrient runoff, general storm Water runoff and runoff from snowy climates where road de-icing salts are applied. The chemicals may be cations, anions, molecules or agglomerations on the order of one thousand or fewer molecules,so long as a soluble micro-granule is formed. More exotic and harmful elements of TDS are pesticides arising from surface runoff. Certain naturally occurring TDS arise from the weathering and dissolution of rocks and soils. The USA has established a secondary water quality standard of 500 – 1000 mg/l to provide a palatability of drinking water.
TDS are differentiated from total suspended solids (TSS) in that the latter cannot pass through a sieve of two micrometers and yet are indefinitely suspended in solution. The term “settleable solids” refers to material of any size that will not remain suspended or dissolved in a holding tank not subject to to motion, and excludes both TDS and TSS. Settleable solids may include larger particulate matter or insoluble molecules.
Natural sources of iron and manganese are more common in deeper wells where the water has been in contact with rock for a longer period of time. In coal mining regions of the state, these metals may also occur from both deep and surface mining activities. Iron and manganese often occur together in groundwater but manganese usually occurs in much lower concentrations than iron.
Both iron and manganese are readily apparent in drinking water supplies. Both impart a strong metallic taste to the water and both cause staining. Water coming from wells and springs with high iron and/or manganese may appear colorless initially but orange-brown (iron) or black (manganese) stains or particals quickly appear as the water is exposed to oxygen.
Ultraviolet water purification (UV) lamps produce UV-C or germicidal UV, radiation of much greater intensity than sunlight. Almost all of a UV lamps output is concentrated in the 254 nanometers (nm) region in order to take full advantage of the germicidal properties of this wavelength. Most UV systems are combined with various forms of filtration, as UV light is only capable of killing microorganisms such as bacteria, viruses, molds, algae, yeast, oocysts like cryptosporidium and giardia.
UV light generally has no impact on chlorine, VOCs, heavy metals, and other chemical contaminants. Nevertheless, it is probably the most cost effective and efficient technology available to eliminate a wide range of biological contaminants from the water supply. Recent testing has also shown that UV can be effective at destroying certain VOCs, although we would not specifically recommend the technology for VOC reduction.
UV water treatment offers many advantages over other forms of water treatment for microbiological contaminants. Most importantly, it does not introduce any chemicals to the water, it produces no bi-products, and it does not alter the taste, pH, or other properties of the water. Accordingly, in addition to produce safe drinking water, it is not harmful to piping systems.
Reverse Osmosis (RO) is a water purification technology that uses a semipermeable membrane to remove ions, molecules, and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pressure, a colligative property, that is driven by chemical potential differences in the solvent, a thermodynamic parameter. Reverse Osmosis can remove many types of dissolved and suspended species from water, including bacteria, and is used in both industrial processes and the production of potable water. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be selective, this membrane should not allow large molecules or ions through the pores, but should allow smaller components of the solution to pass freely.
The normal osmosis process, the solvent naturally moves from an area of low solute concentration, through a membrane, to an area of high solute concentration. The driving force for the movement of the solvent is the reduction in the free energy of the system when the difference in solvent concentration on either side of the membrane is reduced, generating osmotic pressure due to the solvent moving into the more concentrated solution. Applying an external pressure to reverse the natural flow of pure solvent, thus, in reverse osmosis. The process is similar to other membrane technology applications. However, key differences are found between reverse osmosis and filtration. The predominant removal mechanism in membrane filtration is straining, or size exclusion, so the process can theoretically achieve perfect efficiency regardless of parameters such as the solutions pressure and concentration. RO also involves diffusion, making the process dependent on pressure, flow rate, and other conditions. RO is also known for its use in drinking water purification from sea water, removing the salt and other effluent materials from the water molecules.