There are 3 different categories of ways of cleaning water: 1) Filtering, 2) Changing the properties and 3) distillation (evaporation/condensation).
Regardless of type, shape and size – filters do the same thing: Holding things back on one side of a membrane and letting smaller things pass through the given pore size. That means that all filters have a certain lifespan before clogging – and then they need cleaning/exchanging.
These filters come in many different types, ranging from your coffee filter, to sandfilters, to various membranes.
Activated carbon is particularly good at adsorbing organic compounds. Some carbon filters even work as a particle filter.
The ability to hold back dissolved contaminants is called adsorption. The efficiency of the carbon filter depends on particle and pore size, surface area, surface chemistry, density and hardness. Quality manufacturers have different qualities and even dedicated filters for certain usages.
- Carbon filters are almost mandatory for improving taste and smell of water.
- Simple, economical maintenance. Typically an inexpensive filter cartridge needs to be changed every few months to a year, depending on water usage and the manufacturer’s recommendation.
- Carbon filters are prone to bacteria growth, just like any other filter.
- They will not filter out salts, minerals, metals and other dissolved components
Reverse Osmosis (RO) – household/sub counter
Reverse Osmosis is a filter technology with tiny pores in a membrane. To get water molecules to pass, high pressure is needed – from a few bars in a sub counter filter to several hundreds of bars in industrial applications. Ro is today the preferred desalination technology on an industrial scale.
Advantages (household RO systems):
- RO significantly reduces salt, most other inorganic material present in the water, and some organic compounds. With a quality carbon filter to remove any organic materials that get through the filter, the purity of the treated water approaches that, produced by distillation.
- Bacteria and vira are usually removed by properly functioning RO units, but any defect in the membrane would allow these organisms to flow undetected into the “filtered” water – so they are not recommended for use on biologically unsafe water.
- RO systems can purify more water per day than distillers and are less expensive to operate (but will not last as long).
- RO units make only a few gallons of treated water a day.
- RO systems waste water. 3 to 6 portions of “waste” water are flushed down the drain for each portion of filtered water produced.
- Some pesticides, solvents and other volatile organic chemicals (VOCs) are not removed by RO.
- RO membranes are sensitive to the feed waters ph; amount of contaminants; particles; temperature and pressure. If any of these factors are off – the RO-filter will not work properly.
- Although RO filters do not use electricity, they depend on a relatively high water pressure to force the water molecules through the membrane. This means that power on demand must be available all the time.
- Damaged membranes are not easily detected, so it is hard to tell if the system working as it should. Even new ones.
- The performance goes down from day 1 and it will eventually clog.
This is a relatively new technology with promising aspects. Aquaporins, also called water channels, are integral membrane proteins from a larger family of major intrinsic proteins that form pores in the membrane of biological cells, mainly facilitating transportation of water between cells. The cell membranes of a variety of different bacteria, fungi, animal and plant cells contain aquaporins through which water can flow more rapidly into and out of the cell than by diffusing through the phospholipid bilayer.
The technology is quite new (2003) and first filters are now on the market (2018).
2) Changing water properties
Unlike filtration, these methods change the contents in water – but do not remove them.
Ultra Violet “filtration”
UV light effectively destroys bacteria and viruses. So, leading contaminated water through a certain energy level of UV light, will kill and/or disrupt the organism’s genetic material.
It makes sense to use this simple technology in the final stage of a water cleaning system, just to make sure that if any living matter should grow inside the system/piping/dispensers/bottles etc – then an UV-light is a good extra security.
- No toxic byproducts introduced
- Leaves no smell or taste in the treated water
- Requires very little contact time
- Microorganisms are destroyed
- Many pathogenic microorganisms are killed or rendered inactive.
- Does not affect minerals in water
- UV radiation works fine, as long as the water is not too dirty (high turbidity).
- UV light is not effective against any non-living contaminant, lead, asbestos, many organic, chemicals, chlorine, etc.
Ozone is a naturally occurring component of fresh air. It can be produced by the ultraviolet rays of the sun reacting with the Earth’s upper atmosphere (which creates a protective ozone layer), by lightning or it can be created artificially with an ozone generator.
The ozone molecule (O3) contains three oxygen atoms whereas the normal oxygen molecule contains only two. Ozone is a very reactive and unstable gas before it reverts back to oxygen. Ozone is the most powerful and rapid acting oxidizer man can produce and will oxidize all bacteria, mould and yeast spores, organic material and viruses given sufficient exposure.
- Ozone is primarily a disinfectant that effectively kills all biological contaminants.
- Ozone also oxidizes and precipitates iron, sulfur, and manganese so they can be filtered out of solution.
- Ozone will oxidize and break down many organic chemicals including many that cause odor and taste problems.
- Ozonation produces no taste or odor in the water. Since ozone is made of oxygen and reverts to pure oxygen, it vanishes without a trace once it has been used.
- Ozone does not remove dissolved minerals and salts.
In an emergency, boiling is the best way to kill parasites, vira or bacteria.
- Bacteria/vira in the water will be killed.
- Some volatile organic compounds will evaporate
- Nothing is removed from the water.
- High energy demand
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.
Chlorine in water is over three times more effective as a disinfectant against Escherichia coli than an equivalent concentration of bromine, and over six times more effective than an equivalent concentration of iodine.
- Very effective
- Bad taste
- Related to a number of cancer types
3) Nature’s way: Distillation
Nature has provided water cleaning since…ever. The water cycle is what is keeping us alive and what makes all life possible. Collecting water vapor is what it is all about. Rain. Same-same.
Distillation is the core technology of any WaterStillar system:
- Distillation at high temperatures and normal pressure produces ultra pure water.
- Distillation removes close to everything in water nitrates, chloride, and salts. Pathogens as well.
- No drop in quality over time – As long as the distiller is kept clean and is working properly.
- No filter cartridges to replace, unless a carbon filter is used to remove volatile organic compounds.
- Distillation takes time and makes a smaller amount of water compared to other technologies.
- Distillers require periodic descaling of the boiler
Generally, dehumidifier water (including AC’s) is considered a rather clean kind of greywater: not suitable for drinking, but acceptable for watering plants. The water may contain trace metals from solder and other metallic parts. The trace metals may pose a danger if used on edible plants, as they can bioaccumulate. However, the water is usable for irrigation of non-edible plants.
Various pathogens, including fungal spores, may (or will) accumulate in the water, particularly due to its stagnancy. Unlike in distilled water production, the water is not boiled, which would kill pathogens (including bacteria).
Food-grade dehumidifiers, also called atmospheric water generators, are designed to avoid toxic metal contamination and to keep all water contact surfaces clean. The devices are primarily intended to produce pure water, and the dehumidifying effect is viewed as secondary to their operation. Still, the working principles lead to water, that needs careful post-treatment to be used for drinking (carbon, UV, ozone etc).
- No pipes and plumbing.
- Helps with a dry indoor climate in the house
- Both pre- and post filters are necessary.
- Prone to biofouling
- Few liters per day, drinking purposes only