What is clean water?
It depends. Most people will know that water is H2O. Fewer will know that water can contain just about any known matter on earth and is the basis for living things too.
So, to define clean water it is important to look at the usage. Exampels: Water for pharmaceutical process water, drinking, irrigation and washing are measured and defined completely differently. Drinking water is by far not clean enough for "water for injection" - and irrigation water can hold all kind of nutrients and be perfect after a rough treatment in a sewage plant.
To be more pragmatic , the USGS defines clean, safe water as “water that will not harm you if you come in contact with it.”
Going further into what clean water is, most countries have directives for water, look here: EU, US, WHO etc These guidelines about how much of a given contaminant is allowed, changes over time as knowledge grows.
On top of these guidelines, other non-governmental organizations try to raise awareness of water issues. In the US, EWG is a good example - and they claim that safe drinking water has far lower maximum limits than in the above directives.
Over time limits also change - as knowledge and insight grows. Today, we know that contaminants are endless in numbers and that we do not know how they affect our health. When we then add the cocktail effect - we will most likely never quite understand fully where the limits should be for contaminant X.
Example: Today we know that nitrate can be directly related to colon cancer - and that science show us that a safe limit is in the range of 0,4 to 1,4 mg/l. Right now the max limit in EU's drinking water directirve is 50 mg/l.
How to clean water
There are 3 ways of cleaning water: 1) Filtration, 2) Changing the properties and 3) Distillation.
Filtration: Water passes through a filter and the size of the filters holes determine what is being held back. Just think of a coffe filter.
Changing the properties is to add something (chemicals, radiation, magnetic fields, etc etc) into water that then changes the properties in the water. Best example would be chlorination that kills bacteria.
Distillation is evaporation of a solid (water) into a gas and then condensing it back into a solid (water). Contaminants that do not evaporate, is then left behind. Example: Sea water is evaporated into clouds that falls like rain.
An oversimplified way of showing how distillation and filtration compare: Filters clog up over time and will therefore be less effective as they do what is expected: Holding back contaminants. Flushing and eventually changing filters is required.
Distillation will also need maintenance in the form of removing the left behind contaminants. This is either done mechanically or chemicaly (descaling with an citris acid typically). Main point is to notice that the quatlity of the distilled water is constant over time.
How to keep water clean
It is not good enough only to clean water. It is equally as important to keep water clean. Once you have clean water (straight out of a new filter or a still), the waters purity will be comprimised.
Any kind of distribution of water is a weakness. The container (eg. a plastic bottle) will leak chemicals and a dstribution network will have bacteria growth inside.
Migration of contaminants
Water is a great solvant and almost any material will cause migration of contaminants into the water. That is why you should choose a glass bottle and not a plastic one.
Any water test around the world will have a bacteria test for e coli and for slowly growing bacteria. Bacteria multiply when conditions are right and when they have time. Any open container with water will collect airborne virus and bacteria. Any non-sterile container will grow bacteria when water is added. The “risk” of infected water is similar to any other food that is not kept, handled, stored in a proper way.
Biofouling is referred to as the unwanted deposition and growth of biofilms and is almost impossible to avoid in moist/wet surroundings. Any water system will have biofouling, including WaterStillar. Biofouling can occur in an extremely wide range of situations, from the colonisation of medical devices to the production of ultra-pure, drinking and process water and the fouling of ship hulls, pipelines and reservoirs. Although biofouling occurs in such different areas, it has a common cause, which is the biofilm. Biofilms are the most successful form of life on Earth and tolerate high amounts of biocides.
There are a number of ways to keep control over biofouling, here are 3 commonly used in the public water supply:
Water chlorination is the process of adding chlorine (Cl2) or hypochlorite to water. This method is used to kill certain bacteria and other microbes in tap water as chlorine is highly toxic. In particular, chlorination is used to prevent the spread of waterborne diseases such as cholera, dysentery, and typhoid.
Ozonation alternative to chlorination is more cost effective but energy intensive. It involves ozone being bubbled through the water, breaking down all parasites, bacteria, and all other harmful organic substances. However, this method leaves no residual ozone to control contamination of the water after the process has been completed. The advantage of chlorine in comparison to ozone is that the residual persists in the water for an extended period of time. This feature allows the chlorine to travel through the water supply system, effectively controlling pathogenic backflow contamination. In a large system this may not be adequate, and so chlorine levels may be boosted at points in the distribution system, or chloramine may be used, which remains in the water for longer before reacting or dissipating
UV treatment leaves minimal residue in the water. In water, UV generates ozone in situ and thus has many of the advantages of ozone disinfection. However, ultraviolet germicidal irradiation alone (as well as chlorination alone) will not remove toxins from bacteria, pesticides, heavy metals, etc. from water.
Biofouling will occur in a matter of hours/days under the right circumstances. So the solution is to have water cleaning device as close to the point of use and then maintaining the device according to instructions and the feed water quality. Filters are a commonly used device and they must be periodically replaced otherwise the bacterial content of the water may actually increase due to the growth of bacteria within the filter unit.
WaterStillar (and other tabletop distillers) including a carbon pre- or post filter can claim to clean water to the highest possible degree. But still, the piping from the system to the tap must be cleaned periodically – and therefore also kept as short as possible.