Before considering the almost infinite possibilities of solving water harvesting and waste water problems it is important to first gain a basic understanding of water. What makes it up, how it will behave in certain situations and the potential pitfalls encountered when dealing with water. Below is a brief outline of some of the basics regarding water in general and a few important things to remember when dealing with it.

The chemical composition of water is (H2O) which means 2 Hydrogen atoms and 1 Oxygen atom combine to make up one molecule of water.

Water is at its most dense at 4 degrees celcius. It gets lighter as it gets colder (ice will float on water) and will get lighter as it heats up also (hot water floats on top of cold water in a hot water unit).

Potable water - AS/NZS 3500.0 (2003)

Potable water is water that is fit for human consumption. It should have the following characteristics;

• Clear and perfectly transparent. Colourless or bluish when observed through a depth of one metre.
• Free from;
  • Sediment or suspended matter.
  • Organic matter - Microscopic organisms
  • Inorganic matter - Dissolved minerals
  • Diseases
• Potable water should be palatable (not brackish or salty), well aerated and odourless.

Water and the PH Scale

The PH scale is a scientific measure of the acidity or alkalinity of a liquid. The scale ranges from 0 to 14.

Water must be kept slightly alkaline in a piping system to avoid corrosion of metal and concrete pipes used to distribute water throughout the mains and house supply.

The Water Cycle

The water cycle consists of three stages. Evaporation, condensation and precipitation. This process has continued throughout the globe since time began and will continue to do so regardless of the impact humans have had on the earth. Below is a brief explanation of the three stages water goes through as it travels around the earth and into our homes.

• Evaporation - At any one point in time a portion of the water on earth is travelling from the ground into the air through the process of evaporation. It evaporates into the air as a water vapour (colourless and odourless dry gas). As the water evaporates the impurities are left behind. The main source for evaporation are our oceans, however water also evaporates from plants and animals as well.
• Condensation - After water has evaporated into the atmosphere it condenses to form raindrops. These condensed water particles are so small that over 100,000 of them can be contained in a single raindrop. These newly formed droplets join together with others to form the clouds we can see from the ground. Winds blow these clouds around the earth until the water droplets cool and can no longer be supported in the air. These clouds then begin to disintegrate and the water falls as precipitation (rain).
• Precipitation - Water then falls onto the ground, into streams, lakes or the ocean. Most of th water will eventually end up back out in the ocean to restart the water cycle all over again. Water will pick up a few impurities during this process but with the exception of salty sea water it is generally fit for human consumption.

Naturally occuring pollution in water.

During the process of condensation and precipitation water will pickup some naturally occuring pollutants that need to be dealt with before water is considered to be potable. These pollutants fall into three general categories:

• Substances in suspension (Turbidity)- These are solids that are attracted into the water supply and do not dissolve into the water. This makes them fairly easy to remove. Common supensded pollutants are;
  • Silt
  • Sand
  • Clay

• Dissolved Substances (Inorganic Matter)- These are naturally occuring minerals that have been dissolved into the water supply to form a solution. The fact that they are dissolved into solution makes them a little harder to remove than suspended solids. Common dissolved pollutants are;
  • Iron
  • Magnesium
  • Zinc

• Microscopic Life Forms (Organic Matter) - These are viruses and bacteria that have found a home in the water supply. Most of these need to be removed however not all are harmful to humans. Common forms of organic pollutantd are;
  • Viruses
  • Bacteria
  • Algae
  • Aquatic marine life

Water Treatment

It is the responsibility of your local water authority to treat catchment water before it is considered safe to drink (potable) and distributed throughout the local water supply. The is a multi stage process designed to specifically target the different types of pollutants mentioned above. The water goes through a process of screening, flocculation,
PH correction, sterilisation and fluoridation to ensure that it is safe.

• Screening - This is the first stage in the chain and is where water passes through a screen to remove large objects that have made their way into the water supply and would quickly destroy the facilities responsible for the subsequent stages of water treatment.

• Flocculation - This is a process whereby a coagulant is added to the water supply causing small particles in the water to attract together (floc) and settle to the bottom of the body of water.

• Filtration - This process happens after flocculation and is where the water passes through a variety of filter mediums (sand, gravel, crushed coal etc.) to remove the particle formed during the flocculation process.

• PH Correction - Because raid is slightly acidic and this would soon render our distribution networks useless through corrosion of pipes lime is added to the water supply to return it to the desired PH level (between 7 and 7.5).

• Sterilisation - Is where organic pollutants are killed through the addition of chlorine to the water. This is in small enough quantities to not affect the newly established PH of our water however it kills and inhibits the growth of harmful bacteria.

• Flouridation - Not all water supplies go through this final stage however the health benefits of adding flouride to drinking water have been well established. Flouride in drinking water has been proved to assist with the prevention of tooth decay.