Why Filter Your Water?
Water filtration is one of the most effective and least expensive ways to solve equipment fouling and scaling problems caused by dirty water. Heat exchangers, molds, pipes, tubing, sensors, monitors, and other parts become fouled when dirt particles in the water settle out on warm surfaces.
Any water source that is used for drinking may have physical and chemical contaminates such as sand, silt, algae, worms, and snails, making the water unsafe for drinking. In many situations membranes and cartridge filters are used to rid the water of contaminants. This causes too many scheduled and unscheduled shutdowns for maintenance, as well as manual cleaning and replacement of screens, bags, cartridges, and membranes, costing thousands of rupees.
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 (colloidal sol) suspended form. Generally the operational definition is that the solids must be small enough to survive filtration through a sieve the size of two micrometer. Total dissolved solids are normally discussed only for freshwater systems, as salinity comprises some of the ions constituting the definition of TDS. The principal application of TDS is in the study of water quality for streams, rivers and lakes, although TDS is not generally considered a primary pollutant (e.g. it is not deemed to be associated with health effects) 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, 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 stormwater 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 total dissolved solids arise from the weathering and dissolution of rocks and soils. The United States has established a secondary water quality standard of 500 mg/l to provide for palatability of drinking water.
Total dissolved solids are differentiated from total suspended solids (TSS), in that the latter cannot pass through a sieve of two micrometres 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 motion, and excludes both TDS and TSS. Settleable solids may include larger particulate matter or insoluble molecules.
Measurement of TDS
The two principal methods of measuring total dissolved solids are gravimetry and conductivity. Gravimetric methods are the most accurate and involve evaporating the liquid solvent to leave a residue that can subsequently be weighed with a precision analytical balance (normally capable of .0001 gram accuracy). This method is generally the best, although it is time-consuming and leads to inaccuracies if a high proportion of the TDS consists of low boiling point organic chemicals, which will evaporate along with the water. In the most common circumstances inorganic salts comprise the great majority of TDS, and gravimetric methods are appropriate.
Electrical conductivity of water is directly related to the concentration of dissolved ionized solids in the water. Ions from the dissolved solids in water create the ability for that water to conduct an electrical current, which can be measured using a conventional conductivity meter or TDS meter. When correlated with laboratory TDS measurements, conductivity provides an approximate value for the TDS concentration, usually to within ten-percent accuracy.
Total Dissolved Solids
Elevated total dissolved solids can result in your water having a bitter or salty taste; result in incrustations, films, or precipitates on fixtures; corrosion of fixtures, and reduced efficiency of water filters.
Sources of Total Dissolved Solids (Minerals)
in Drinking Water
Water is a good solvent and picks up impurities easily. Pure water -- tasteless, colorless, and odorless -- is often called the universal solvent. Dissolved solids" refer to any minerals, salts, metals, cations or anions dissolved in water. Total dissolved solids (TDS) comprise inorganic salts (principally calcium, magnesium, potassium, sodium, bicarbonates, chlorides and sulfates) and some small amounts of organic matter that are dissolved in water.
TDS in drinking-water originate from natural sources, sewage, urban run-off, industrial wastewater, and chemicals used in the water treatment process, and the nature of the piping or hardware used to convey the water, i.e., the plumbing.. In the United States, elevated TDS has been due to natural environmental features such as: mineral springs, carbonate deposits, salt deposits, and sea water intrusion, but other sources may include: salts used for road de-icing, anti-skid materials, drinking water treatment chemicals, stormwater and agricultural runoff, and point/non-point wastewater discharges.
In general, the total dissolved solids concentration is the sum of the cations (positively charged) and anions (negatively charged) ions in the water. Therefore, the total dissolved solids test provides an qualitative measure of the amount of dissolved ions, but does not tell us the nature or ion relationships. In addition, the test does not provide us insight into the specific water quality issues, such as: Elevated Hardness, Salty Taste, or Corrosiveness. Therefore, the total dissolved solids test is used as an indicator test to determine the general quality of the water. The sources of total dissolved solids can include all of the dissolved cations and anions, but the following table can be used as a generalization of the relationship of TDS to water quality problems.
CaCO3, MgCO3 etc - Associated with hardness, scale formation, bitter taste.
NaCl, KCl - Salty or brackish taste, increase corrosivity.
Potential Health Effects
An elevated total dissolved solids (TDS) concentration is not a health hazard. The TDS concentration is a secondary drinking water standard and therefore is regulated because it is more of an aesthetic rather than a health hazard. An elevated TDS indicates the following:
1)The concentration of the dissolved ions may cause the water to be corrosive, salty or brackish taste, result in scale formation, and interfere and decrease efficiency of hot water heaters; and
2)Many contain elevated levels of ions that are above the Primary or Secondary Drinking Water Standards, such as: an elevated level of nitrate, arsenic, aluminum, copper, lead, etc.
Total Dissolved Solids (TDS): In a laboratory setting, the total dissolved solids is determined by filtering a measured volume of sample through a standard glass fiber filter. The filtrate (i.e., filtered liquid) is then added to a preweighed ceramic dish that is placed in a drying oven at a temperature of 103 C. After the sample dries, the temperature is increase to 180 C to remove an occluded water, i.e., water molecules trapped in mineral matrix. Total dissolved solids means the total dissolved (filterable) solids as determined by use of the method specified in Title 40 of the Code of Federal Regulations (40 CFR) Part 136.
High total dissolved solids may effect the aesthetic quality of the water, interfere with washing clothes and corroding plumbing fixtures. For aesthetic reasons, a limit of 500 mg/l (milligrams per liter) has been established as part of the Secondary Drinking Water Standards.
An approximation of the Total Dissolved Solids:
A. The total dissolved solids concentration can be related to the conductivity of the water, but the relationship is not a constant. The relationship between total dissolved solids and conductivity is a function of the type and nature of the dissolved cations and anions in the water and possible the nature of any suspended materials. For example, a NaCl solution and KCl solution with a conductivity of 10000 umhos/cm will not have the sample concentration of NaCl or KCl and they will have different total dissolved solids concentration. Conductivity is measured through the use of a meter and is usually about 100 times the total cations or anions expressed as equivalents and the total dissolved solids (TDS) in ppm usually ranges from 0.5 to 1.0 times the electrical conductivity.
Total Dissolved Solids can be measured in the field using an electronic pen. Many of these devices actually measure the conductivity of the water, i.e., the ability of the water to carry a charge, and not the actual total dissolved solids. These devices than calculate the total dissolved solids assuming that the primary dissolved minerals are either a combination of NaCl or KCl. Therefore, the measurement of total dissolved solids by these devices are not an accurate measure, but an approximation. If you are thinking of using these devices for a project, I would recommend purchasing a conductivity pen which measures the conductivity of the water.
B. Student Total Dissolved Solids Test (Student Use Only - Not for Regulatory Use)
1. Filter your water sample through a rinsed and dried glass fiber filter. Collect the filtrate (liquid) and rinse water in a flask. The minimum sample volume should be 100 ml and you should use at least 3 rinses of 20 to 30 ml volumes. (Recording your data)- Record weigh of container and volume of filtrate - do not include the volume of the rinse water). The rinse water should be deionized water. Do not touch container with bare hands.
2.Transfer the filtrate to a ceramic or glass Pyrex container. The container should be weighed to the nearest 0.0000 g and place the container in the drying oven, which is set at 103 C. Add the filtrate to the container and allow the sample to stay in the oven at 103 C for 24 hours. If possible, increase the temperature of the drying oven to 180 C and allow the sample to dry for up to 8 hours. Remove the container - Remember it is very hot. After removing from the drying oven, the sample should be placed in a desiccator to cool in a dry air environment for at least 3 to 4 hours. If the sample cooled in a moist environment, the sample would increase in weight because of the addition of water vapor from the air. Remember the sample is very hot and can melt plastic.
Do not touch container with bare hands.
3.After the container cools, reweigh the container at least three times to the nearest 0.0000 g (Recording your data)
4.Subtract the initial weight (in grams) of the empty container from the weight of the container with the dried residue to obtain the increase in weight. Then do the following:
A- Weight of clean dried container (0.0000 grams)
B- Weight of container and residue (0.0000 grams)
C- Volume of Sample (do not include rinse water ) ( 100 mls)
Concentration (mg/L) = ((B - A)/ C)* (1000 mg/g) * (1000 ml/L)
A= 100.0001 g
B = 100.0020 g
C = 100 mls
Concentration (mg/L) = ((100.0220 - 100.0001)/ 100) * 1000 * 1000 = 219 mg/L
If you have a private water supply, you can have the water tested for total dissolved solids and/or conductivity Most water testing laboratories offer total dissolved solids tests for a fee, including the Environmental Quality Center.