These tests cover the physical properties, mineral balance, disinfection and other chemistry of drinking water, well water, process water and environmental samples. Concentrations are reported in milligrams per liter (mg/L) unless a test says otherwise. Each test below names the reference method and how the measurement works.
| Test | Method |
|---|---|
| pH | EPA Method 150.1 |
| Temperature | EPA Method 170.1 |
| Conductivity and resistivity | Standard Methods 2510 B |
| Salinity | No method number listed |
| Turbidity | EPA Method 180.1 |
| Color | Standard Methods 2120 B |
| Odor | EPA Method 140.1 |
| Specific gravity | Pycnometer or digital density meter |
| Oxidation-reduction potential (redox) | Platinum electrode against a reference electrode |
| Alkalinity | Standard Methods 2320 B |
| Acidity | Standard Methods 2310 |
| Carbon dioxide | Standard Methods 4500-CO2 D |
| Hardness | Calculated from calcium and magnesium by EPA Method 200.7 |
| Langelier saturation index | Calculated index |
| Bromate | EPA Method 300.1 |
| Chlorine residual, chloramines and chlorine demand | No method number listed |
| Dissolved oxygen | EPA Method 360.1 |
| Cyanide: total, weak acid dissociable and amenable to chlorination | Standard Methods 4500-CN E (total), 4500-CN I (weak acid dissociable), 4500-CN G (amenable to chlorination) |
| Fluoride by electrode and colorimetry | Standard Methods 4500-F C and 4500-F E |
| Sulfide | Standard Methods 4500-S2- F |
| Silica | Standard Methods 4500-SiO2 E |
| Ferrous iron | Standard Methods 3500-Fe B |
| Hexavalent chromium | EPA Method 7196 |
| Phenols | EPA Method 420.4 |
| Surfactants (MBAS and CTAS) | Standard Methods 5540 C (MBAS) and 5540 D (CTAS) |
| Tannin and lignin | Standard Methods 5550 B |
| Chlorophyll a | Standard Methods 10200 H |
| Volatile organic acids | Ion chromatography |
| Glycols (ethylene, diethylene and propylene glycol) | EPA Method 8015, modified |
| Oxidizable substances in purified water | ASTM D1193 |
| Suspended sediment concentration (SSC) | ASTM D3977 |
Physical properties
EPA Method 150.1: pH is measured with a glass electrode and a meter calibrated with standard buffers, with temperature compensation; the result is reported with the sample temperature. A laboratory result describes the sample as received. Reported in pH units.
EPA Method 170.1: measured with a calibrated thermometer or temperature sensor. Temperature describes the water at the time it is measured, so it is most useful when taken on site. Reported in degrees Celsius (°C).
Standard Methods 2510 B: the sample’s ability to carry an electric current is measured with a conductivity cell and reported at 25 °C in microsiemens per centimeter (µS/cm). Conductivity rises with the amount of dissolved ions. Resistivity, usually asked for with purified water, is the reciprocal of conductivity and is reported in ohm-centimeters.
Salinity is the total amount of dissolved salts in water. It is usually derived from conductivity and temperature and reported on the practical salinity scale, which has no units and is close to grams of salt per kilogram of seawater. It is used for brackish water, seawater, estuaries and brines.
EPA Method 180.1, nephelometry: light scattered at 90 degrees by particles in the sample is measured and compared with formazin standards. Reported in nephelometric turbidity units (NTU).
Standard Methods 2120 B, visual comparison: the sample is compared with platinum-cobalt color standards. Turbidity is removed first when true color is needed; without that step the result is apparent color. Reported in color units.
EPA Method 140.1, threshold odor: the sample is diluted with odor-free water until its odor can only just be detected by smell. The result is the threshold odor number, the dilution ratio at that point.
Measured with a pycnometer or a digital density meter: the density of the sample is divided by the density of water at a stated temperature. Used for brines, process liquids and wastes. Reported as a ratio without units.
Measured with a platinum electrode against a reference electrode. The reading shows whether conditions in the water are oxidizing or reducing. Reported in millivolts, with the reference electrode stated.
Alkalinity, hardness and scaling
Standard Methods 2320 B, titration: the sample is titrated with standard acid to set pH end points, 8.3 for phenolphthalein alkalinity and about 4.5 for total alkalinity. Bicarbonate, carbonate and hydroxide alkalinity can be calculated from the results. Reported as mg/L calcium carbonate (CaCO3).
Standard Methods 2310, titration: the sample is titrated with standard sodium hydroxide to set pH end points (3.7 and 8.3). Reported as mg/L calcium carbonate (CaCO3).
Standard Methods 4500-CO2 D: free carbon dioxide is calculated from the sample pH and alkalinity rather than measured directly. Reported as mg/L carbon dioxide (CO2).
EPA Method 200.7: calcium and magnesium are measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), and hardness is calculated from them. Reported as mg/L calcium carbonate (CaCO3).
A calculated index from the measured pH, total dissolved solids, alkalinity and calcium, and the water temperature. A positive index means the water tends to deposit calcium carbonate scale; a negative index means it tends to dissolve calcium carbonate. It indicates a tendency and is not a direct measurement of corrosion.
Disinfection
EPA Method 300.1, ion chromatography. This is a separate method from the EPA 300.0 anions above; it is used for bromate, a by-product formed when water containing bromide is disinfected, mainly with ozone. See the anions section for bromide. Reported as mg/L.
Free chlorine is the hypochlorous acid and hypochlorite left in water after chlorination; total chlorine also includes combined chlorine, mainly the chloramines that form when chlorine reacts with ammonia. Systems that disinfect with chloramines follow total chlorine or monochloramine. Chlorine demand is the amount of chlorine the water uses up over a set contact time: the chlorine added minus the residual left. Residuals are expressed as mg/L chlorine (Cl2). Chlorine residual changes soon after sampling.
Dissolved oxygen and inorganic tests
EPA Method 360.1, membrane electrode: oxygen passes through a membrane to an electrode, and the current produced is proportional to the oxygen concentration. Reported as mg/L oxygen.
Total cyanide, Standard Methods 4500-CN E: the sample is distilled from strong acid to release cyanide from most of its complexes, and the cyanide collected is measured by colorimetry (chloramine-T with a pyridine-barbituric acid reagent). Weak acid dissociable cyanide, Standard Methods 4500-CN I, uses a milder, weakly acidic distillation that releases free cyanide and the weaker metal complexes but not the strong iron cyanide complexes. Cyanide amenable to chlorination, Standard Methods 4500-CN G, is total cyanide measured on two portions, one of them chlorinated first; the difference is the cyanide that chlorination destroys. Reported as mg/L cyanide (CN).
Besides ion chromatography in the anions section, fluoride is measured by Standard Methods 4500-F C, an ion-selective electrode read in a buffered sample, and Standard Methods 4500-F E, an automated colorimetric (complexone) method. Reported as mg/L fluoride.
Standard Methods 4500-S2- F, iodometric: sulfide reacts with a measured excess of iodine in acid, and the iodine left over is titrated with thiosulfate. Water results are reported as mg/L sulfide. Solid samples can also be tested; the preparation and reporting basis are confirmed when you order.
Standard Methods 4500-SiO2 E, automated: silica reacts with molybdate to form a yellow molybdosilicic acid, which is reduced to a blue compound and measured. The method measures molybdate-reactive silica. Reported as mg/L silica (SiO2).
Standard Methods 3500-Fe B, phenanthroline: ferrous iron forms an orange-red complex with 1,10-phenanthroline that is measured by spectrophotometry. The reducing step used for total iron is left out, so only the ferrous form is counted. Ferrous iron oxidizes in air, so contact us before sampling. Reported as mg/L iron.
EPA Method 7196, colorimetric: in acid solution, hexavalent chromium reacts with diphenylcarbazide to form a red-violet color measured by spectrophotometry. Only the hexavalent form reacts, so the result differs from total chromium in a metals test. Water results are reported as mg/L. Solid samples can also be tested; the preparation and reporting basis are confirmed when you order.
Organic indicators
EPA Method 420.4: after distillation, phenolic compounds react with 4-aminoantipyrine to form a colored product measured by automated colorimetry. Phenols differ in how strongly they react and some substituted phenols do not react, so the result is total recoverable phenolics, reported as mg/L phenol.
Anionic surfactants, Standard Methods 5540 C: they form a blue ion pair with methylene blue that is extracted into chloroform and measured by spectrophotometry, as methylene blue active substances (MBAS). Nonionic surfactants, Standard Methods 5540 D: they are separated from the sample by gas stripping (sublation) and measured as cobalt thiocyanate active substances (CTAS). Both results count every substance that reacts, not one named surfactant. Reported as mg/L.
Standard Methods 5550 B, colorimetric: tannins, lignins and other hydroxylated aromatic compounds reduce a phosphotungstic-phosphomolybdic reagent to a blue color. The result includes every compound that reacts and is reported as mg/L tannic acid.
Standard Methods 10200 H: algae are collected on a filter and their pigments extracted into acetone; chlorophyll a in the extract is measured by spectrophotometry or fluorometry and can be corrected for pheophytin, its breakdown product. The result is reported per volume of water filtered.
Measured by ion chromatography as acetate and other short-chain organic acids, and reported as mg/L acetic acid. The test is used to follow anaerobic digesters and other biological treatment processes.
A modified form of EPA Method 8015: the sample is injected into a gas chromatograph, the glycols are separated, and each is measured with a flame ionization detector. Reported as mg/L for each glycol.
A test from the ASTM D1193 reagent water specification: the water is acidified, a small amount of potassium permanganate is added, and the pink color is checked after the time the specification sets. Oxidizable material, mostly organic, removes the color. The result shows whether the color is kept.
Sediment
ASTM D3977: the sediment in the whole sample is separated by filtration or evaporation, dried and weighed. Because the whole sample is used, SSC includes sand that a subsample for total suspended solids can miss. Reported as mg/L.
Some results, such as pH, temperature, chlorine and dissolved oxygen, change soon after a sample is collected and are best measured on site or as soon as possible. Contact us for containers and sampling instructions before you collect the sample.
The method numbers on this page follow the published EPA and Standard Methods designations. These references describe the methods; the TNI LAMS registry lists each method’s code and revision.
Questions about a sample or a method, call 360-967-7010 or email [email protected].
