Every drop counts

Filtration, ion exchange, separation and disinfection are four broad categories of technologies available to purify water. Within these, there are further sub-technologies like micro-filtration, ultra-filtration, reverse osmosis, and disinfection. Depending on the water quality, separation (membrane) and disinfection technologies are used to create safe drinking water free from excessive contaminants and salts dissolved in water (TDS) and/ or microorganisms to adhere to WHO standards.

Reverse Osmosis (RO) is an effective way to treat water with higher than permissible levels of TDS, which may also contain substances such as fluorides and arsenic. A high TDS level is normally associated with hardness and an undesirable taste. In many cases, the main driver of RO usage is the noticeable change in taste post treatment. It has a pleasant taste, akin to bottled water. It is important to remember that most RO membranes reduce TDS by 90%. So if the TDS is 600 mg/ml to begin with, the treated water will have a TDS of 60. Ideal TDS levels should be in the range of 60-80 mg/ml. Ground water often contains microorganisms as well, so disinfection post RO is often good protection. (The primary job of an RO membrane is to separate the dissolved impurities, not disinfect).

When the source of water is surface, filtration and disinfection technologies normally suffice to make the water safe. A chemical-based gravity purifier or a chemical-free UV purifier does a good job of disinfection. Adding an RO to treat surface water which has low TDS to start with, is normally unnecessary and akin to antibiotic treatment being administered for a common cold.

Test first

If your source of water is ground water of unknown chemical composition you are first required to test the water as per IS 10500, which is the Indian standard for safe drinking water. Based on the report the appropriate treatment can be decided. It could be a simple chemical-based gravity filter or a well-designed UV purifier if the water is chemically potable and just requires to be disinfected or an RO system when water has excess of dissolved chemicals beyond the permissible range. Normally most people suggest an RO purifier if your TDS is greater than 500 ppm.

Expert advice

It is advisable to let a water treatment specialist go through your analysis report and suggest the right treatment required. The water treatment specialist would be able to suggest any additional pre-treatment, which may be required. For example excessive iron/ arsenic/ hardness/ fluoride in water may be required to be treated before the RO.

In case there is a reason to suspect microbiological contamination, a micro test in a lab or a home check kit available in the market will reveal if the water is micro-biologically unsafe.

Jargon buster

Next, see what companies are offering. With jargon being thrown at you, check the meaning and implications of systems, which have RO UV, RO UV UF, TDS Controller, etc. Some of these are unnecessary and increase the cost of the equipment and maintenance, without adding any real value.

A TDS controller is nothing but a simple Bypass Valve (bypassing the membrane) meant for controlling the mix between RO water (devoid of minerals) and regular tap water, which contains minerals. This is done so that you are not drinking water with very low TDS. So the question is, did you need to use an RO purifier in the first place?

Consider implications

Know the pros and cons of each technology. For example, in an RO water purifier as much as 75-80% of the water is rejected and only 20-25% is used for drinking. In many non-electric, gravity-based storage type water purifiers, chlorine may be the chemical used for purification.

In a UV purifier, know that hard water will not become soft and that the cartridges and UV lamp need replacement at regular intervals, besides regular cleaning. Understand the costs of maintaining each system and cost of consumables.

Calculate pressure

Understanding whether you have sufficient water pressure while using an online water purifier is important. Online water purifiers normally need a pressure of between 10-40 PSI (pounds per square inch) for them to work effectively.

An easy way to calculate the pressure in your tap is to see how many floors you are from the terrace from where water is distributed by gravity. So if you are in a 10 story building and you live on the 8th floor, then your water pressure is likely to be 10 PSI, because every 10 feet from the top is equivalent to 5 PSI. If you live on the first floor, then the pressure in your tap will be around 45 PSI. In that case, a pressure reducing valve may be required along with the online water purifier.

For homes with very low pressure, a booster pump will help or alternately a UV purifier which works on loft tank pressure can be opted for.