Water Quality Indicators

Investigating the Earth’s Hydrosphere: Water Quality Indicators

Introduction

• Water is vital for life, animals, and the environment.

• Maintaining water quality is essential for various purposes like human consumption and industrial use.

• Determining water quality requires more than just visual inspection.

Water Quality Parameters

• Water quality parameters are grouped into three types:

  • Chemical

  • Physical

  • Biological

Chemical Parameters

• Basic chemical characteristics include:

  • pH

  • Dissolved Oxygen (DO)

  • Hardness

  • Nitrates

  • Phosphates

pH (Potential of Hydrogen)

• pH represents the acidity or alkalinity (basicity) of water.

• The pH scale ranges from 0 to 14.

• pH < 7: Acidic

• pH > 7: Basic (alkaline)

• pH = 7: Neutral (pure distilled water)

• pH is related to the balance between hydrogen ions (H+) and hydroxide ions (OH-).

  • More H+ than OH-: Acidic

  • More OH- than H+: Basic (alkaline)

  • Equal H+ and OH-: Neutral

• The pH scale is logarithmic; a one-step change implies a tenfold change in H+ concentration.

  • Example: Water with a pH of 4 is ten times more acidic than water with a pH of 5.

• Aquatic organisms may be harmed by water with a pH of less than 4.8 or greater than 9.2.

• Most freshwater fish prefer a pH of 6.5 to 8.4.

• WHO standards for drinking water: 6.5 to 8.5.

Dissolved Oxygen (DO)

• DO is the amount of free oxygen (O2) dissolved in water.

• It's critical for aquatic plants and animals.

• Measured using a dissolved oxygen meter or DO meter (optical or electrochemical sensor).

• Ways oxygen gets into water:

  • Wind blowing over water surfaces

  • Aquatic plants and algae during photosynthesis

  • Water movement (splashing waves)

• Rivers and streams typically have higher DO concentrations than lakes due to faster aeration.

• Oxygen's solubility in water is poor.

• DO is affected by:

  • Temperature: Cold water holds more DO than warm water.

    • At 4 °C, pure water can hold about y13.2 ppm DO at 100 percent saturation.
      4
      {}^
      {o}C = 13.2 ppm

    • At 25 °C, pure water can hold about 8.4 ppm at 100 percent saturation.
      25
      {}^
      {o}C = 8.4 ppm

  • Salinity: Waters with high salt concentrations retain less DO than pure water.

• Impacts of DO concentration (ppm = parts per million):

  • 5-6 ppm: Sufficient for most aquatic species

  • < 3 ppm: Stressful to most aquatic species

  • < 2 ppm: Fatal to most species

• Terms:

  • Hypoxia: Low dissolved oxygen levels in water (from 2 ppm down to 0.5 ppm)

  • Anoxia: Absence of oxygen; dissolved oxygen levels in water below 0.5 ppm

Total Phosphates

• Phosphates (PO4 3-) are naturally occurring forms of phosphorus (P) in rivers, but usually in small quantities.

• Lower phosphate levels are generally better.

• Total phosphates include organic (part of living plants and animals) and inorganic phosphates (ions bonded to soil particles and phosphates present in laundry detergents).

• ppm (parts per million) is used to express small concentrations of dissolved substances:

  • 1 ppm = 1 \frac{mg}{L}

• ppb (parts per billion) is an even smaller concentration:

  • 1 ppb = 1 \frac{\mu g}{L}

• Phosphates are required nutrients for plant growth.

• Excess can cause eutrophication (excessive plant and algae growth), decreasing water transparency.

• When plants and algae die, aerobic bacteria consume DO, potentially causing death to fish and other aquatic organisms.

• Excess phosphates in water may come from erosion, agricultural, storm water, residential, and industrial runoff.

• Phosphate Level Limits:

  • River draining into a natural lake: 0.05 ppm

  • Natural lake: 0.025 ppm

  • River that is not flowing into a lake: 0.1 ppm

Nitrates

• Nitrates (NO3 –) are naturally occurring forms of nitrogen and are more abundant than phosphates.

• Like phosphates, excess nitrates can cause algal bloom and reduce water transparency.

• The nitrogen cycle balances nitrate levels naturally.

• Excess nitrates come from agricultural and industrial runoff.

• Philippine National Standards for Drinking Water (PNSDW) of 2017 limits nitrate concentration to 50 ppm for drinking water.

• High nitrate concentrations may cause methemoglobinemia (blue baby syndrome) in bottle-fed infants.

Hardness

• Water hardness measures the concentration of dissolved minerals like calcium, magnesium, strontium, iron, and manganese.

• Water containing these minerals is referred to as “hard” because it requires more soap/detergent to create a lather.

• Hard water is usually alkaline or basic.

• Total hardness is represented as ppm of calcium carbonate (CaCO3).

• Hardness Level as a measure of CaCO3 concentrations:

  • Soft: 0 – 60 ppm

  • Moderately Hard: 60 – 120 ppm

  • Hard: 120 – 180 ppm

  • Very Hard: Greater than 180 ppm

Total Dissolved Solids (TDS)

• TDS indicates the amount of material dissolved in water.

• These materials are often inorganic solids with a small amount of organic content, both natural and anthropogenic.

• The PNSDW limit for TDS in drinking water is 300 ppm.

• High TDS levels can cause undesirable tastes and laxative effects, making water unsuitable for aquatic life and crop irrigation.

Physical Parameters

• Physical characteristics of water include:

  • Temperature

  • Color

  • Taste and Odor

  • Turbidity

  • Solids

Temperature

• Water temperature affects:

  • Rates of biological processes (metabolic rates of aquatic organisms, sensitivity to pollution, parasites, and diseases)

  • Chemical processes (rate of photosynthesis, gas solubility)

• Increase in water temperature can:

  • Reduce dissolved oxygen capacity.

  • Promote biological activities.

    • Increase the activity of cellular enzymes, increasing metabolic functions in most aquatic organisms.

    • Increase photosynthetic activity in most algae.

• Changes in water temperature are influenced by:

  • Changes in season and weather

  • Industrial discharge

  • Removal of shading vegetation

  • Groundwater influx

Turbidity

• Turbidity represents the amount of light scattered in water due to suspended particles.

• It determines how far light can travel through the water.

• Suspended particles include clay, silt, fine organic and inorganic substances, soluble colored organic compounds, planktons, and other microorganisms.

• A sudden increase in turbidity may be caused by runoff from land.

• Relative turbidity can be measured using a Secchi disk.

  • Low turbidity: the disk is visible far below the surface.

• Accurate measurement is done using a turbidimeter (nephelometer) and is expressed in nephelometric turbidity units (NTUs).

• The PNSDW maximum allowable level of turbidity for drinking water is 5.0 NTU.

Conductivity

• Conductivity is the ability of water to conduct electricity.

• It is connected to the concentration of dissolved solids: the more dissolved solids, the more ions present, which means the more electrical current can be conducted.

• Measured using a conductivity meter and is expressed in microsiemens per centimeter (µS/cm).

• The target water quality range is 0 to 70 µS/cm.

Color

• Pure water is colorless.

• The presence of color indicates suspended particles and organic matter.

• Color can be reported as:

  • Apparent color: Color of the whole water sample (dissolved and suspended components).

  • True color: Measured after filtering the water sample to remove all suspended material.

• Color is graded on a scale of 0 (clear) to 70 color units.

• Pure water has 0 color units.

• Possible Water Colors and Their Cause:

  • Blue: transparent; low level of accumulated dissolved materials; low rate of productivity

  • Yellow/brown: significant amount of dissolved organic materials, humic substance from soil, peat, or decaying plant material

  • Red: certain algae

  • Green: presence of phytoplankton and other algae

  • Mixture of colors: soil runoff

Taste and Odor

• Pure water has no taste, but substances like zinc or foaming agents can give it a taste.

• Chemical Component and Their Corresponding Taste:

  • Chloride, sulfate: salty taste

  • Copper, iron, zinc: metallic taste

  • Foaming agent: bitter taste

  • Manganese: bitter metallic taste

• Pure water is odorless.

• Dissolved substances influence the odor.

• Decayed organic substances: fouling smell

• Inorganic substances: earthy smell

Biological Parameter

• Biological parameters are the organisms found in water such as fecal coliform bacteria.

Fecal Coliform Bacteria

• Most bacteria are useful, but some are harmful, causing diseases.

• Coliforms and fecal streptococci are used to test for disease-causing microorganisms.

• They are called “fecal” indicators because they live in the intestinal tract of humans and other warm-blooded animals.

• Fecal coliform bacteria are not harmful themselves, but their presence indicates the water might contain harmful microorganisms.

• Large amounts of fecal coliform bacteria can give water a murky appearance, bad smell, and lowers DO level.

• Sources of fecal coliform bacteria include wastewater treatment plants, domestic and wild animal manure, and storm runoff.

• The USEPA standard for drinking water is 0 coliform per 100 mL (0 col./100 mL) of water.

Summary

• Water quality assessment involves checking physical, chemical, and biological parameters against regulatory standards.

• It is important to maintain water quality for various uses.

Chemical Parameters:

• pH: Acidity or alkalinity of water.

• Dissolved oxygen (DO): Amount of free oxygen (O2) in water.

• Total phosphates (PO43–): Total amount of phosphates in water.

• Nitrates (NO3 –): Total amount of nitrates in water.

• Hardness: Concentration of dissolved minerals in water.

• Total dissolved solids: Total amount of materials contained in water.

Physical Parameters:

• Temperature: How hot or cold the water is.

• Turbidity: Cloudiness or murkiness of water.

• Conductivity: Ability of water to conduct electrical current.

• Color: Indicates the presence of suspended particles and dissolved matter.

• Odor: Indicates the presence of organic and inorganic substances.

Biological Parameter:

• Fecal coliform bacteria: Indicates the presence of pathogens in water.