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Water Quality Primer


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Water Quality

What do we mean by water quality?

Water quality is defined in terms of the chemical, physical and biological content of water. The water quality of rivers and lakes changes with the seasons and geographic areas, even when there is no pollution present. There is no single measure that constitutes good water quality. For instance, water suitable for drinking can be used for irrigation, but water used for irrigation may not meet drinking water guidelines. The quality of water appropriate for recreational purposes differs from that used for industrial processes.

What are the key factors that influence water quality?

Many factors affect water quality. The natural water quality of groundwater in aquifers is related to the quality of recharge water, the mineralogy of soils and aquifer sediments, the residence time in the ground water flow system, and the presence of nearby saline water. However,  the primary influence on groundwater quality (as well as surface water quality) is the contamination brought about by human activity.

Urban stormwater, agricultural runoff, domestic wastewater, industrial wastewater, and hydrologic modifications are the major sources of water pollution in Florida. Other threats include nitrates from dairy and other livestock operations, fertilizers and pesticides in stormwater runoff, toxic chemicals in leachate from hazardous waste sites, and erosion from construction sites, unpaved roads, and farm fields. Septic tank leachate contributes to the degradation of many water bodies by adding nitrate nitrogen, bacteria, viruses, and synthetic organics used in household cleaning products and septic tank cleaners. Industrial activities can increase concentrations of metals and toxic chemicals, add suspended sediment, increase temperature, and lower dissolved oxygen in the water. Gasoline storage areas (including service stations) may have leaks and spills of petroleum products.  Roadways contribute petroleum pollutants leaked from vehicles and metals from exhaust fumes.  Older sanitary landfills, whose leachate may contain many different chemicals at relatively high concentrations, also pose a threat.

How do we measure water quality?

The quality of water is determined by making measurements in the field or by taking samples of water, suspended materials, bottom sediment, or biota, and sending them to a laboratory for physical, chemical and microbiological analyses. For example, acidity (pH), color and turbidity (a measure of the suspended particles in the water) are measured in the field. The concentrations of metals, nutrients, pesticides and other substances are measured in the laboratory.

Another way to obtain an indication of the quality of water is biological testing. This test determines, for example, whether the water or the sediment is toxic to life forms or if there has been a fluctuation in the numbers and kinds of plants and animals. Some of these biological tests are done in a laboratory, while others are carried out at the stream or lake.

What is good quality drinking water?

Good quality drinking water is free from disease-causing organisms, harmful chemical substances, and radioactive matter. It tastes good, is aesthetically appealing, and free from objectionable color or odor.

It should be noted that there is a difference between "pure water" and "safe drinking water". Pure water, often defined as water containing no minerals or chemicals, does not exist naturally in the environment. Under ideal conditions, water may be distilled to produce "pure" water. Safe drinking water, on the other hand, may retain naturally occurring minerals and chemicals such as calcium, potassium, sodium or fluoride which are actually beneficial to human health and may also improve the taste of the water. Where the minerals or chemicals occur naturally in concentrations that may be harmful or displeasing, then certain water treatment processes are used to reduce or remove the substances. In fact, some chemicals are actually added to produce good drinking water; the best examples of chemical addition are chlorine used as a disinfectant to destroy microbial contaminants, or fluoride used to reduce dental cavities.

How can we be sure that water is safe to drink?

Since 1974, when Congress passed the original Safe Drinking Water Act, EPA has set  uniform nationwide minimum standards for drinking water. State public health and environmental agencies have the primary responsibility for ensuring that these federal drinking water quality standards, or more stringent ones required by the state, are met by each public water supplier. Local governments, public water systems, the states, and EPA work together towards the goal of ensuring that all public water supplies are safe. For more information, go to the EPA web site Water on Tap: What You Need To Know.

For households on private wells, state and local health departments usually have some standards for the drinking water, but it is generally up to the homeowner to maintain the quality of the drinking water. In Florida you can get information on how to safeguard well water supply from the county extension office, the county public health department, the Florida Department of Environmental Protection, and the Home*A*Syst web site.

If we could boil all the water we consume, could we eliminate pollution?
No. Boiling water kills germs but will not remove chemicals.
Is chlorine in the water supply necessary, and could it become a health hazard?

Chlorine was introduced as a disinfectant in water treatment around the turn of the century. It has since become the predominant method for water disinfection. Apart from its effectiveness as a germicide, it offers other benefits such as color removal, taste and odor control, suppression of algal growths, and precipitation of iron and manganese. In addition, chlorine is easy to apply, measure and control. It is quite effective and relatively inexpensive.

Chlorine as a disinfectant in water treatment can be a health hazard if its concentration or the concentrations of certain by-products (e.g., trihalomethanes, a chlorinated organic compound) are greater than the allowed by the EPA. If the maximum acceptable concentrations are exceeded, the authorities responsible for public health should be consulted for the appropriate corrective action.

Some people say that you shouldn't pour solvents and other household chemicals down the drain because they pollute the rivers and lakes. Is that true? How else can I get rid of them?

While chemical household products are generally safe for the uses they are designed for, some may become harmful to the environment as they accumulate in it. For this reason you should not put these products down the drain. Most sewage treatment facilities are not capable of removing such toxic substances. Anything put into the storm sewers is going directly to the receiving lake or river completely untreated. So, before you dump anything down the drain, remember that you or others may be drinking it some day.

Some cities and communities in Florida sponsor either occasional or permanent hazardous waste collection program.  If your community does not sponsor such a program, contact the DEP Hazardous Waste Management Section (904/488-0300).

As a responsible consumer how can I tell if the products I buy are potentially harmful to the environment?

Most household chemical products and pesticides sold in the United States have warning labels. These labels tell us whether the product is flammable, poisonous, corrosive or explosive. The labels usually also give first aid instructions. Read the label to find out how to use the product safely and what precautions to take for its disposal.

What happens to water that drains out of our home?

Sewers collect the liquid waste and discharge it into lakes, streams or the ocean. Most, but not all, municipalities treat their sewage using mechanical and/or biological processes before discharging it. Regardless of the process, sewage treatment plants concentrate the sewage into a solid called sludge, which is then utilized on agricultural land, disposed of in a landfill site, or incinerated. For a detailed description of the wastewater treatment process, visit the USGS Water Science for Schools web site.  Residents of rural areas, may have individual septic systems (shown in the diagram to the left) or have sewage collected by truck.

Septic tank diagram

Eutrophication is a form of pollution. What is a eutrophic lake?

Eutrophication is the process of becoming better nourished either naturally or artificially. In terms of a lake, eutrophication occurs naturally with the gradual input of nutrients and sediment through erosion and precipitation resulting in a gradual aging of the lake. Humans speed up this natural process by releasing nutrients, particularly phosphorus, into rivers and lakes through municipal and industrial effluent and through increased soil erosion by poor land use practices. Eventually, a lake has high nutrient concentrations and dense growths of aquatic weeds and algae. These plants die and decompose causing depletion of dissolved oxygen in the water. This process often results in fish kills and changes in a lake's fish species. Ultimately, eutrophication will fill the lake with sediment and plant material. Lake Apopka, Lake Okeechobee and the Florida Everglades have suffered from eutrophication. This resulted from agricultural and urban runoff coupled with the inability of these waters to flush themselves due to altered drainage.








Algae bloom in Lake Okeechobee


Source:  South Florida Water Management District

How does irrigation affect water quality?

Irrigation affects water quality in different ways, depending upon the original water quality, the type of soil, the underlying geology, the type of irrigation, the crop grown, and the farming methods used.

Although a large portion of irrigation water is used by plants or evaporates from the soil (evapotranspiration), part of it is returned to the source. As is often the case with water use, when the water returns to the stream or water body, the quality has been lowered. The water that runs off the fields carries with it sediments, fertilizers, herbicides, pesticides (if these chemicals are used on the fields), and natural salts leached from the soil and enters rivers, lakes and groundwater supplies.

Is the discharge of cooling water from electrical power plants a form of pollution?

Yes, it is called thermal pollution. Water is used for condenser cooling and then discharged into nearby rivers, streams, or coastal environments. However, most of these facilities have controls on the maximum temperature of their discharge waters, and many of them use cooling ponds or towers.

Thermal pollution, when not regulated, can be a problem. Artificially heated water can promote algae blooms, threatening certain species of fish and otherwise disturbing the chemistry of the receiving water body and its estuarine life. When this water is not reused by industries or for heating in nearby communities, large amounts of energy and potential dollar savings are lost.

How good is our water?

Overall, the majority of Florida’s surface waters are of good quality, but problems exist around densely populated urban areas, primarily in central and southern Florida. In rivers, nutrient enrichment, low dissolved oxygen, organic matter, siltation, and habitat alteration degrade water quality. In lakes, the leading problems result from metals and other toxics, ammonia, and nutrients. In estuaries, nutrient enrichment, habitat alteration, and siltation degrade quality. Special state concerns include widespread mercury contamination in fish, bacterial contamination in the Miami River, and algal blooms and extensive die-off of mangroves and sea grasses in Florida Bay.

Data from over 1,900 wells in Florida’s ambient monitoring network indicate generally good water quality, but local ground water contamination problems exist. Agricultural chemicals, including aldicarb, alachlor, bromacil, simazine, and ethylene dibromide (EDB) have caused local and regional (in the case of EDB) problems. The Florida DEP has documented more than 400 instances of groundwater contamination from leaking gasoline pipes or storage tanks and found groundwater contamination at 156 hazardous waste sites in the state.

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Last Revised on: 11/20/2007