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Water Filters

Purifying Water Using Water Filters

Most people want the luxury of pure water flowing from their taps. They want to have a shower or clean their teeth with the knowledge that they will not get sick from bacteria or minerals in the water. If possible they want to be able to drink the water directly from the tap.

In many parts of the world the purity of water cannot be guaranteed and people look towards filtering water to purify it.

There are many different kinds of filter available, everything from sand filters to remove particles floating in the water to carbon filters that absorb metals and other minerals and Ultra Violet light treatments that kill bacteria. Reverse osmosis is a relatively new technology used for purifying water.

Here we discuss the different filtration methods available.

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Drinking water from the tap

water filters

To most of us the idea of drinking water from a tap is a distant memory from a past life living in a western country. To look after our health we have had to adapt to life in a country where contamination of our water supplies is the rule rather than the exception. We drink bottled water, avoid cold drinks with ice from unknown sources, don’t swallow the water from the shower and certainly don’t clean our teeth in it.

The major cause of this problem in many parts of the world is the contamination of ground water from septic tanks which are often still the most common way of disposing of toilet and other waste water from houses. A properly constructed septic system requires a drainage field into which semi processed waste from the septic tank is discharged where it can soak into the ground and where bacteria continue the process of breaking down the waste. Drainage fields are a luxury that simply cannot be afforded in the urban areas of Indonesia where houses are often built very close to each other.

To provide clean water for drinking and cleaning our teeth we usually buy water in large plastic ‘gallon’ containers but there are, of course, alternatives.

Small kitchen bench mounted units

You may, for example, buy a small filtration unit that mounts on or under a bench top close to a tap. These units tend to use replaceable cartridges to filter your tap water to “potable” (drinking water) standard. They generally have a low output and require regular replacement of the cartridges which don’t come cheap.

Reverse Osmosis Systems

Another alternative is to buy a small scale “reverse osmosis” plant. Reverse osmosis works by pumping water through a very fine semipermeable membrane which extracts the particles and bacteria that contaminate the water. Reverse osmosis is a highly effective way of purifying water and can even deal with saltwater removing up to 95% of the salt. Indeed, reverse osmosis is so effective that it has been accused of being unhealthy for humans leaving the water “dead” having stripped out many of the naturally occurring minerals that our bodies need for good health.

As pure water runs through the membrane impurities on the pressurised side of the membrane build up into a concentrate that is then drained to waste. Some users report that these systems waste a significant proportion of the water. The membrane requires high pressure to force the water through typically anything from 30 to 1,200 psi depending on the application and a special water pump is required. Reverse osmosis systems usually have series of steps with other filtration processes in addition to the membrane itself. Reverse osmosis systems don’t come cheap and are generally well engineering pieces of equipment. A typical household system is likely to cost at least $3,000.

Low cost drinking water filtration

It is not difficult or expensive to have drinking quality “potable” water running through the taps in our houses. There is a reasonable costing and effective solution that can provide potable (drinkable) water to your whole house. The system uses filtration units that are installed in the water supply to the house. Such a system will cost between 6 and 10 million rupiah ($600 to $1,000).

Sand Filters

Firstly the water is passed through a sand filter which removes large contaminants such as sediments and particles from the water. This is not only a first stage cleaning process but also helps to prolong the life of the next filtration process.

Carbon Filters

The water then passes through a carbon filter to remove mineral contamination. Carbon filters are effective in removing organic contaminants from water which are the usual culprits for taste, odour and colour problems. Carbon filters can remove or reduce many volatile organic chemicals, pesticides and herbicides, as well as chlorine, benzene, trihalomethane compounds, radon, solvents and hundreds of other man-made chemicals found in tap water. Carbon filters are NOT generally successful at removing dissolved inorganic contaminants or metals such as minerals/salts, antimony, arsenic, asbestos, barium, beryllium, cadmium, chromium, copper, fluoride, mercury, nickel, nitrates/nitrites, selenium, sulfate, thallium, and certain radio nuclides. Reverse osmosis can remove these contaminants.

UV (Ultra Violet) steriliser

Finally the water is passed through a UV filter, a tube with Ultra violet lights inside that kills any bacteria in the water most importantly the ecoli and choliform that comes from sewerage contamination.

Do low cost systems work?

Do these systems work? Well, yes they do and very effectively. A good friend of mine runs a restaurant and he uses a lot of water in the kitchen for washing vegetables and dishes. He decided he would install a water filtration system to provide washing up water. The system was installed and, being a restaurant, the government came and tested the water. The results were surprising. The system using sand and carbon filters with a UV steriliser was found to supply water that was cleaner than the bottled water he was buying.

Hard water is a very common problem in many places and it should be noted that these types of system do not make hard water soft. To do this it is necessary to remove calcium carbonate which is in solution in the water. Reverse osmosis can soften hard water. We can also use a water softener.


Regular maintenance is essential for these systems. They need regular backwashing involving the pumping of water backwards through the filters to dislodge and wash away contaminants taken from the water. This backwashing process is often carried out manually however automated systems are readily available that have electronic systems to automatically switch on the backwashing process. These controls can be either timer controlled or triggered by sensing when the water pressure increases due to the filter becoming clogged up. Automated systems are a good idea in a country where regular maintenance is carried out when someone remembers to do it.

Carbon filters require regular replacement of the carbon to keep them effective.

Ultra Violet filters are very effective at killing bacteria however they are susceptible to failure particularly the light tubes blowing due to power fluctuations. It is important to check the UV filters regularly to make sure the UV tubes are still working.

Water pressure is an important issue, and as we have already said reverse osmosis systems require special pumps that supply high water pressure to pump the water through the membrane. A normal household water system could be expected to operate at between 2 and 4 bar (30 to 60 psi) and this will be enough to pump water through a sand and carbon filtration system. Swimming pools systems tend to use water pumps that deliver high volume flows of water at lower pressures, around 2 bar 30 psi). A swimming pool sand filter cannot, therefore, be used for filtering water for normal house usage simply because it is not designed to take the higher pressures found in household systems.

Laboratory test your water

As a final comment, it is a good idea to get your water checked in a laboratory to see what contaminants you have and their levels. Obviously bacteria such as ecoli and toxic minerals such as lead or mercury should not be in your water.

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Copyright © Phil Wilson September 2012
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