Water

Potable water

Definition

• water that is safe to drink

Criteria

• number of dissolved substances must be low
• pH between 6.5 to 8.5
• Contains no microorganisms

Surface water

Definition

• bodies of water exposed at their surface

Examples

• Lakes
• Rivers
• Reservoirs

Where does it come from

• In the U.K. it comes from rain

Advantages

• Easy to access
• Refills itself very easily

Disadvantages

• With too much sun exposure, water can easily dry up

Ground water

Definition

• Water stored underground

Examples

• Aquifers - permeable rock stored underground which traps water

Fresh water

• 1) Using a wire mesh, pour water through to filter out large matter
• 2) Next pass water through a bed of sand and gravel to filter out smaller matter
• 3) Sterilise water to kill any microorganisms and bacteria

Sterilising techniques

• Bubble through chlorine
• Expose to ozone
• Expose to ultraviolet light

Desalination

Distillation

• Same process as simple distillation but with much larger quantities of water
• Overall idea is too collect water vapour and condense to form pure distilled water

Reverse Osmosis

• Salty water is passed through a membrane

• Only water molecules can pass through

• filtering out all other matter

• You are left with pure distilled water

Disadvantages of desalination

• Requires a lot of energy
• This can be extremely impractical and expensive

Waste water

Types

• Domestic
• Industrial
• Agricultural systems

Domestic waste

• House hold waste from: Showers, skinks, toilets
• Water flushed down the drain travels through the sewers to sewage treatment plants

Agricultural systems

• Nutrient run off from fields
• Animal waste from plants

Industrial waste

• Factories that make and use chemicals

Sewage treatment

• process is still easier than desalination thus some countries rely on waste water treatment to provide potable water

Screening

• remove all large matter, typically by passing it through a mesh

Sedimentation

• Let the sewage set in a settlement tank to undergo sedimentation
• You are left with both sludge and effluent which can be separated into two separate tanks

Biological Breakdown By Microorganisms

• Aerobic - pump oxygen into tank containing the effluent so matter is broken down by aerobic digestion until water is safe enough to be released back into the environment
• Anaerobic - keeping the tank containing sludge sealed to prevent contact with oxygen thus matter is broken down by anaerobic digestion. In the process methane is produced which can be burned as an energy source while the remnants can be used as a fertiliser seeing as they are rich in nutrients

Removing toxins

• adding chemicals
• ultraviolet radiation