Water quality is determined by testing whether ten primary factors meet a specific parameter for the type of water being tested. Appropriate levels will vary by the intended use of the water. For example, drinking water will have different acceptable qualities than fish tank water.
The most common quality factors tested include:
pH levels of water are expressed in terms of how acidic or alkaline (basic) it is. This measurement is determined by how H+ (positive hydrogen ions) are balanced with OH- (negative hydroxide ions).
The pH scale ranges from the strongly acidic 0 to the highly basic 14, where there’s a high concentration of OH-. Pure water has a pH of 7—a perfect balance.
In ponds and lakes, pH levels are impacted by age and any chemicals being discharged into the water. Most bodies of water like this start highly basic and then become more acidic over time. Organic material builds up and then decays, which leads to the formation of CO2 (carbon dioxide). The weak acid that’s formed when this mixes with water is known as carbonic acid.
Fish survive well in waters with pH levels as acidic as 5 and as alkaline as 9. Seawater responds better to acid waste due to the way the various salts protect it.
Linked to pH levels but standing separately, the alkalinity of water measures the amount of water with acid-neutralizing properties.
pH expresses the strength of a base or acid, whereas alkalinity demonstrates the buffering strength of the solution. Alkalinity prevents the pH levels of the water from changing by absorbing the acid.
Alkalinity is essential for marine life. It ensures the water won’t be as vulnerable to acid rain and protects against changes in pH levels. Rocks are a prime source of natural alkalinity. Phosphates, silicates, and borates might also contain traces of alkalinity. Each property serves some purpose.
Granite has no minerals linked to alkalinity, so granite-rich areas suffer from inadequate buffering capacity. Limestone, on the other hand, is laden with carbonates, and so has an elevated buffering capacity.
Remember: Do not confuse alkalinity with pH levels. Alkalinity is not a pollutant and is an overall metric of water quality.
Nitrites and Nitrates
The element nitrogen comes in different forms, including:
The air we breathe is composed of 80% nitrogen.
Nitrogen is a critical component of life on many levels and can be found in the cells of all living things. For instance, plants and animals endlessly recycle nitrogen. When combined with carbon, organic nitrogen occurs in proteins and various compounds.
Inorganic nitrogen exists as a gas, combined with hydrogen in the form of ammonia, and it can also take the form of nitrites and nitrates when it’s combined with oxygen.
Nitrites and nitrates occur naturally during the nitrogen cycle.
Nitrites vs. Nitrates
- Nitrites: Nitrites are rapidly converted to nitrates by bacteria. Although only a fleeting presence in the environment, nitrites can bring about brown blood disease in fish. Nitrites can also trigger the production of methemoglobin that impairs the ability of the blood cells to shift oxygen. This problem can be particularly risky with babies. Babies should not consume water when nitrite levels exceed 1mg/l.
- Nitrates: One can commonly find nitrates in fertilizer. Nitrates are easily washed into waterways. The core role of nitrates is to promote the growth of water weeds and plankton. Algae should not be allowed to grow too wildly, though, or it reduces oxygen levels to the extent fish will die. Nitrates in the human body can become toxic once in the intestine.
As long as nitrate/nitrogen levels are below 90 mg/l, warm water fish respond well when levels of nitrites are below 0.5 mg/l. With salmon and cold-water fish, the minimum nitrite level should be 0.06 mg/l.
Pure ammonia is colorless and has a remarkably strong smell. It can be manufactured (from hydrogen and nitrogen) or produced (from coal gas).
A robust cleaning agent, ammonia becomes extremely powerful when mixed with water. This fact makes it among the most common household cleaning chemicals.
The chemical formula for ammonia is NH3. This formula refers to a single atom of nitrogen and three hydrogen atoms.
The high nitrogen count of ammonia makes it a superb fertilizer, but unfortunately, ammonia is toxic to fish and other marine life, even if present in low concentrations. Fish can suffer from gill damage with ammonia levels as low as 0.06 mg/l, while fish like salmon or trout can die when ammonia is present in the water in concentrations as small as 0.2 mg/l. Worse, as the pH levels and temperature of water rise, ammonia becomes more toxic to fish.
An ammonia level of 0.1 mg/l or above is indicative of a polluted water body.
Chlorine is a gas that will dissolve readily in water. The distinctive and sharp smell can be detected in concentrations as low as 0.3 parts per million.
It is an effective antiseptic and is routinely added to drinking water in the US. When chlorine is not added to drinking water in other parts of the world, waterborne diseases like cholera and typhoid can quickly strike.
Commonly used to treat wastewater in swimming pools or industrial plants, one can also use multi-purpose chlorine as an efficient bleaching agent, and in low levels, it poses no risk to humans. However, when chlorine is dissolved in water, it’s toxic to fish even in trace amounts.
When water is packed with decaying material, chlorine can end up bonding. This bond forms compounds called THMs (trihalomethanes), which can be carcinogenic.
- Chlorine in Industry: Chlorine can impart a strange taste in canned or frozen foods. It can also interfere with the brightness and smoothness of plated metals. Even low levels of chlorine can impair the quality of paper during manufacturing.
- Chlorine for Irrigation: Since the concentration of chlorine seldom hits levels of 1 mg/l, neither city water, not wastewater used for irrigation should be problematic.
- Chlorine for Fish and Marine Life: Fish can die with chlorine levels as low as 0.1 mg/l, with only the toughest of fish surviving when chlorine levels exceed 0.25 mg/l.
An odorless and colorless gas, carbon dioxide is produced during the breathing cycle of animals and bacteria.
Animals consume and use oxygen, and they expel carbon dioxide. Green plants absorb this carbon monoxide and then harness the process of photosynthesis to yield carbon-rich foods and oxygen.
For green plants, photosynthesis only occurs in the presence of light. This process means that more carbon dioxide enters the water at night. This issue is usually kept in balance by the natural day-night cycle, but if there’s been a spell of cloudy weather, which can negatively impact the ability of plants to photosynthesize, fish are affected in terms of respiration.
Oxygen Dissolved in Water
When oxygen is dissolved in water, it’s known as DO (dissolved oxygen).
Fish can’t split oxygen from compounds like water. Green plants, along with some bacteria, step in to accomplish this through the process of photosynthesis. Green plants produce the vast bulk of the air we breathe. Fully three-quarters of the world’s oxygen is generated by phytoplankton.
Warm water doesn’t contain much oxygen, and when there’s too much marine life or bacteria, DO often occurs. The DO quantity required by fish varies by species, water temperature, state, and pollutants. This number of variables renders it impractical to consider minimum DO levels for fish.
High DO levels in the water makes it taste better. The drawback is the intensification of corrosion in piping.
Phosphorus is an element required for animal and plant growth. Almost all fertilizers contain phosphorus, and this washes into waterways when it rains. It helps encourage the growth of water plants and plankton.
This process is beneficial to fish in terms of lifespan, but too much phosphate can choke up the waterway and use up an excessive amount of oxygen. During the phosphorus cycle, not all phosphates end up recycled.
Phosphates won’t hurt humans unless they’re present in intense concentrations.
In plain English, turbidity refers to how cloudy water is.
How effectively light travels through liquid depends to a large extent on the amount of suspended material that’s in the water. Plankton and soil erosion are the most common causes of turbidity in rivers and lakes.
You can accurately measure turbidity levels using an electronic turbidimeter. For drinking water, the turbidity should not be greater than 0.5 NTUs (nephelometric turbidity units). Water plants need plenty of light for photosynthesis. If light levels are too low and the water is too turbid, photosynthesis can stop with algae dying.
Too much-suspended matter can also clog the gills of fish. Fish won’t be able to see well in turbid water either.
Many variables influence the temperature of the water.
- Color: Dark-colored water absorbs heat more efficiently.
- Depth: Deep waters tend to be colder since they need more time to warm up.
- Latitude: If the climate is colder, the water is likely to be naturally colder
- Shade: Waterways shaded for prolonged periods by overhanging trees tend to be colder.
- Temperature of Effluents: If heated effluents are dumped into the water, the temperature will rise.
- Temperature of Water Supply: The temperature of the water flowing into a lake or river will play a large part in determining the temperature of the lake.
- Time of Year: The temperature of waterway water varies seasonally.
- Volume: The more water is in place, the longer it will take to heat up or cool down.
Fish are cold-blooded and highly sensitive to water temperature changes. A change as little as 2 degrees can cause fish to attempt to relocate!