How to Analyze Water Quality: Key Tests and Parameters

Water is rarely pure. Whether drawn from a river, a borehole, or a municipal supply, it carries dissolved minerals, suspended particles, and chemical signatures that tell a detailed story about its origin, the land it has traveled through, and any pollutants it may have picked up along the way. Water quality analysis is the scientific process of reading that story – using measurable parameters to determine whether water is safe to drink, suitable for irrigation, or capable of sustaining aquatic life. Among the most foundational of these parameters are total solids, pH, and electrical conductivity. Understanding what each measures, how it is tested, and why it matters is essential for anyone working with water resources.

Why water quality analysis matters 🔗

Untested water is an unknown risk. Contaminated drinking water can transmit waterborne diseases, while poor-quality irrigation water can degrade soil structure, damage crops, and reduce yields over time. On the environmental side, altered water chemistry can disrupt aquatic ecosystems, reduce biodiversity, and affect the food chains that depend on healthy water bodies.

According to the World Health Organization, the palatability of drinking water is directly linked to its dissolved solid content – water rated “excellent” contains fewer than 300 mg/L of total dissolved solids, while water exceeding 1,200 mg/L is considered unacceptable. This alone illustrates how closely chemistry and quality are connected. Regular testing against established standards ensures water is fit for its intended purpose, whether that is drinking, farming, or ecosystem support.

Total solids: measuring what water carries 🔗

Total solids (TS) refers to all the material left behind in a container after a water sample is fully evaporated and dried at a defined temperature. As the U.S. Environmental Protection Agency explains, total solids are the sum of dissolved solids and suspended and settleable solids in water. This makes TS a broad but important measure of the overall load of matter a water sample is carrying.

Dissolved solids vs. suspended solids 🔗

Total Dissolved Solids (TDS) are the portion of total solids that pass through a filter with pore sizes of 2 micrometers or smaller. In stream water, dissolved solids consist of calcium, chlorides, nitrate, phosphorus, iron, sulfur, and other ion particles – essentially the minerals and salts that have fully dissolved into the water. Total Suspended Solids (TSS), by contrast, are particles too large to pass through that same filter – silt, clay, algae, plankton, and fine organic debris that remain physically dispersed in the water column.

The distinction matters because each type of solid creates different problems. Higher concentrations of suspended solids can serve as carriers of toxics, which readily cling to suspended particles – a particular concern where pesticides are used on irrigated crops, since contaminant concentrations can increase significantly as irrigation water travels through channels. High TDS, on the other hand, affects the water balance in the cells of aquatic organisms; water with very high dissolved solids can cause cells to lose water through osmosis, while extremely low TDS water can cause them to swell.

The U.S. has established a secondary water quality standard of 500 mg/L for TDS to ensure drinking water palatability. For classification purposes, freshwater is generally defined as having less than 1,500 mg/L TDS, brackish water between 1,500 and 5,000 mg/L, and saline water above 5,000 mg/L.

How total solids are tested 🔗

Total solids analysis cannot be performed in the field – it requires laboratory equipment. According to the American Public Health Association’s Standard Methods for the Examination of Water and Wastewater, TDS is tested by drying filtered water at 103-105°C, while TSS is determined by weighing the dried residue retained on a standard glass-fiber filter. TDS can also be estimated in the field using a conductivity meter, since dissolved ions that contribute to TDS also increase a water sample’s ability to conduct electricity – a relationship that makes electrical conductivity a useful proxy measurement. Samples must be kept refrigerated and analyzed within seven days of collection to prevent biological decomposition of the solids.

pH: the chemical balance of water 🔗

pH is a measure of how acidic or alkaline water is, expressed on a scale from 0 to 14, where 7 is neutral. Values below 7 indicate acidity (more hydrogen ions), while values above 7 indicate alkalinity (more hydroxyl ions). The scale is logarithmic – each unit represents a tenfold difference in ion concentration – meaning a pH of 5 is ten times more acidic than a pH of 6. pH is notably one of the most important physicochemical parameters because it controls the behavior of other water quality parameters as well as metal concentrations in aquatic environments.

pH and aquatic life 🔗

pH is one of the most important environmental factors limiting species distributions in aquatic habitats, with optimal ranges for most aquatic organisms falling between pH 6.5 and 8. Outside this range, physiological stress increases rapidly. Elevated pH can damage the gills and skin of aquatic fish; if pH rises above 10, aquatic organisms can die from ammonia poisoning. At low pH, the solubility of heavy metals increases sharply, making them more bioavailable and toxic.

pH in natural water bodies is not static. During daylight, aquatic plants and algae consume CO₂ through photosynthesis, raising the pH. At night, they respire and release CO₂, lowering it. The pH of a well-buffered pond may fluctuate between 7.0 and 8.4 over a single day. Human activities such as acid rain, agricultural runoff, and industrial discharges can push pH outside these natural cycles, creating conditions that are difficult for aquatic ecosystems to recover from.

pH and drinking water safety 🔗

The WHO standard for drinking water pH is a range of 6.5 to 8.5. Within this range, water is chemically stable, poses minimal corrosion risk to plumbing, and supports effective disinfection. Acidic water can corrode metal pipes, causing lead, copper, and zinc to leach into the water supply – a significant public health concern in older infrastructure. Highly alkaline water, meanwhile, can cause mineral scaling in pipes and may affect the taste of the water.

pH also directly affects the performance of water treatment processes. When pH increases, the effectiveness of chlorine as a disinfectant decreases, requiring higher doses to achieve the same level of pathogen control – a practical consideration in water treatment plant operations.

How pH is measured 🔗

pH is measured using either electronic pH meters (which measure the voltage difference across a glass electrode sensitive to hydrogen ions) or colorimetric methods (using indicator dyes or test strips that change color depending on acidity levels). Electronic meters provide more precise, continuous readings and are standard in both field and laboratory settings. Regular calibration using buffer solutions of known pH is essential for accurate results.

Electrical conductivity: reading dissolved ions directly 🔗

Electrical conductivity (EC) measures how well water can carry an electrical current, which is directly related to the concentration of dissolved ions present. Pure water is an extremely poor conductor of electricity; it is the dissolved inorganic salts – calcium, sodium, chloride, nitrate, sulfate, and others – that allow current to flow. EC is an important parameter for assessing water quality because it indicates the level of dissolved contaminants and serves as a quick, reliable indicator of overall ionic load.

What conductivity reveals 🔗

Conductivity in streams and rivers is affected primarily by the geology of the area through which the water flows – streams running through granite bedrock tend to have lower conductivity, while those passing through clay soils register higher values. Human activity also leaves a clear signature: a failing sewage system raises conductivity due to the additional chloride, phosphate, and nitrate it introduces, while an oil spill lowers conductivity because organic compounds do not break down into ions. A sudden change in conductivity – in either direction – is therefore a useful early warning sign of pollution.

For freshwater rivers and streams in the United States, conductivity generally ranges from 50 to 1,500 µmhos/cm, with streams supporting good mixed fisheries typically falling between 150 and 500 µmhos/cm. The EPA recommends a maximum conductivity of 1,000 microsiemens per centimeter (µS/cm) for drinking water, though no single national standard currently exists for conductivity alone.

Conductivity and its relationship to TDS 🔗

Conductivity and TDS are closely linked. While TDS measurements are derived from conductivity, some states, regions, and agencies set a TDS maximum rather than a conductivity limit for water quality purposes. In practice, the TDS concentration in mg/L can be estimated by multiplying the conductivity result by a factor between 0.55 and 0.9, a conversion that allows conductivity meters to provide a rapid approximation of dissolved solid load without requiring laboratory evaporation tests. This makes EC one of the most practical and cost-effective tools in routine water quality monitoring.

How conductivity is measured 🔗

Conductivity is measured using an electrical conductivity sensor that determines current flow between two electrodes. Units are typically expressed as microsiemens per centimeter (µS/cm) or millisiemens per centimeter (mS/cm). Temperature significantly affects conductivity readings – warmer water conducts electricity more efficiently – so results are standardized and reported at 25°C to allow consistent comparisons across samples and locations.

How these parameters work together in water quality assessment 🔗

Total solids, pH, and electrical conductivity are not assessed in isolation – they provide the most value when interpreted together. High conductivity, for instance, often points to elevated TDS, which may indicate mineral contamination, agricultural runoff, or saltwater intrusion. Unusual pH readings can flag industrial pollution, acid rain impact, or harmful algal bloom activity. Together, these three parameters form the first tier of water quality screening – a rapid, cost-effective diagnostic layer that guides decisions about whether further testing for heavy metals, pathogens, or specific chemical contaminants is warranted.

For irrigation water specifically, all three parameters are critical. High EC values suggest salinity that can damage crops, while TDS above the 500-1,000 ppm range recommended by the FAO for irrigation may require treatment before use. pH affects nutrient availability in the root zone, with most crops performing best in slightly acidic to neutral soil-water conditions. Monitoring these parameters regularly enables farmers and water managers to make informed decisions about water use, treatment, and conservation.

What do you think? If a water body shows a sudden spike in electrical conductivity alongside a drop in pH, what human activities might you investigate first – and how would you use total solids data to confirm your hypothesis? With increasing agricultural intensification and industrial discharge into freshwater systems, are current water quality testing standards rigorous enough to protect both human health and aquatic ecosystems long-term?

References

1. https://www.who.int/docs/default-source/wash-documents/wash-chemicals/total-dissolved-solids-background-document.pdf
2. https://archive.epa.gov/water/archive/web/html/vms58.html
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4. https://fieldreport.caes.uga.edu/publications/C1276/understanding-laboratory-wastewater-tests-ii-solids-ts-tss-tds-tvs-tfs/
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC8789185/
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8. https://www.epa.gov/system/files/documents/2021-07/parameter-factsheet_ph.pdf
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10. https://atlas-scientific.com/blog/water-quality-parameters/
11. https://archive.epa.gov/water/archive/web/html/vms59.html
12. https://nmtracking.doh.nm.gov/environment/water/PHConductivity.html
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15. https://www.erunwas.com/news-detail/id-229.html