A few months ago, it was time to replace the water purifier at home. The present one was difficult to maintain – the model was discontinued and its replacement parts were no longer available.

We thought it would be a simple task of selecting from one of the popular brands (like Kent or Aquaguard).

Little did we know that it would become a whole big project that required deeper research and evaluation of many alternatives based on criteria. Our task was made easy by the details available at achawater.com – a comprehensive site that covers water purification in great depth.

Typical impurities that need to be removed

As the first step we had to figure out the possible impurities to be removed. Our water is supplied by the municipality in Bangalore (BWSSB).

Here is a list of possible impurities in this water.

Sediment and other particles. Tap water often contains tiny particles of mud, dust, fine sand, clay, rust and other gunk that make the water cloudy, brown or red. Sediment also makes makes the water difficult to swallow and leaves a yukky feeling in the mouth. Some of the sediment may be harmful.

Germs, bacteria, viruses. Tap water can contain living organisms like algae, bacteria, protozoa, pathogens, microbes, viruses, parasites and their cysts (eggs). These micro-organisms often cause typhoid fever, dysentery, cholera, and gastroenteritis. One of the common micro-organism in India is e-coli – a cause of gastroenteritis.

Dissolved Salts. Then there are salts dissolved in water. Some amount of dissolved salt is necessary in drinking water, excess salt (beyond a certain threshold) is considered harmful. Also, some dissolved salts are harmful even in small quantities and need to be removed. The dissolved salts are measured as TDS (or Total Dissolved Salts) and expressed as ppm (parts per million) or as mg/L (milligrams per liter).

There is variation in the threshold for suitable level of TDS. From what I gathered, TDS over 500 ppm is considered unsuitable and TDS below 300 ppm is excellent.

Our criteria for a water purifier

1. Removal of sediments. Our tap water is usually free of sediments. But once in a while we find that the water is red/ brown and has fine dust or rust or mud. This typically happens immediately after some tanks in the supply-chain are cleaned. So, we needed something to remove the sediments.
2. Removal of micro-organisms (bacteria, viruses, parasites and their cysts). We wanted not only to neutralize them, but also wanted make sure that we don’t ingest their carcasses (dead bodies).
3. Taste Enhancer. As the municipal water is treated with chlorine and other chemicals, there is sometimes a faint smell/ taste that is not so nice. We wanted our purifier to remove this smell/ taste.
4. Storage of clean water with automatic cut-out. The purification process is slow, so we wanted the clean water to automatically fill a storage tank (of around 5 liters), from which we could draw out water fast . We also wanted something that will automatically stop the inflow once the tank is filled, so that we don’t have to hang around waiting for the to tank fill up.
5. If possible, we wanted a purifier that did not need electricity for its functioning.
6. Minimal wastage of water. As we extract pure water, we would need to remove the impurities by draining the impure water. We wanted a filter that minimized wastage of water.
7. Simple design and ease of maintenance. We wanted our purifier to have minimal moving parts (e.g., pumps), electronic parts and electrical components, as these increase the complexity and reduce the ease of maintenance.

The total dissolved salts (TDS) in our supply is less than 300 ppm, so there was no need to remove salts.

Purification Technologies Available

Here are the technologies that are currently being used for household water purification in India.

Filters Removing Sediments

Sediment filters remove mud and cloudiness from water. They are usually cartridges containing a fiber based filter housed in a hard plastic casing. The dirt accumulated in the cartridges needs removal, and the cartridges need to be replaced after a pre-defined usage.

UV (Ultra-Violet) Purification

UV water purifier uses ultra-violet light to kill living micro-organisms like organisms  germs, bacteria, viruses, protozoa, and cysts. UV alone does not remove the dead bodies of the micro-organisms.

UV technology needs electricity.

Problems with UV: Sometimes, scales form on the UV bulb, due to heat from the bulb and salt in the water. When the UV bulb is off,   algae or slime can form on  the UV bulb. This could block the UV rays. Therefore, the UV bulb requires periodic servicing.

Membranes Filters

There are multiple types of membranes that are used to filter impurities from water. Each type of membrane has pores that allow water and small particles to pass through and block larger particles. The main difference in different types of membranes is the size of the pores – hence, what is passed through and what is blocked.

The types of membranes are MF (Micro-Filtration), UF (Ultra-Filtration), NF (Nano-Filtration),  and RO (Reverse Osmosis) membranes. Here is what I found about each of membrane type.

MF (Micro-Filtration): Pore size is around 0.1 micron. Will remove particles, parasites and protozoa.

Will NOT remove bacteria or viruses, or dissolved salts.

Does not need water at high pressure. Very little water is wasted.

UF (Ultra-Filtration): Pore size is around 0.02 micron. Will remove particles, parasites and protozoa, bacteria and viruses.

Will NOT remove dissolved salts.

Does not need water at high pressure. Very little water is wasted.

NF (Nano-Filtration): Pore size is around 0.001 micron. Will remove particles, parasites and protozoa, bacteria, viruses and large molecules of dissolved salts. Will remove salts of heavy metals like Arsenic, Lead, Cadmium and Mercury.

Will NOT remove dissolved salts with small molecule size.

Needs water at moderate pressure. Moderate amount of water is wasted.

RO (Reverse Osmosis): Pore size is around 0.0005 micron. Will remove particles, parasites and protozoa, bacteria, viruses and most of the dissolved salts.

Needs water at high pressure. Large amount of water is wasted (around 4 liters of waste per liter of purified water).

All membranes need to be replaced after a certain amount of usage.

Activated Carbon

Passing water through an activated carbon removes toxic organic compounds in water like pesticides and heavy metal organic compounds. It also improves the taste, removes smells and makes cloudy water clear.

Activated carbon filters do not require electricity. These filters have to be replaced periodically (like every six months or a year, depending on the usage).

Our Choice of Technologies

We narrowed the technology to the following combination:

• Pre-filter for removal of sediment / particulate matter. This would also improve the performance and life of the rest of the equipment.
• UF membrane filter. This would remove all parasites, bacteria and viruses, but would not remove dissolved salts. Since our supply did not have excess of dissolved salts, there was no need to remove them. These filters do not require electricity, nor is there much of waste water generated.
• Activated carbon. To remove bad smells and enhance the taste.

We decided not to add UV (utra violet) purifier. The UF membrane would block the viruses – so there was no need to kill them :-).

Our Final Choice

There are many brands that supply UF based filters. We finally chose the model Pureflo UF from Permionics. We selected Permionics because the response from the company representatives and their local agents was fast and all of them seemed knowledgeable. And they were not trying to push the most expensive model.

Pureflo UF  has a sediment filter followed by a UF membrane. It ends with an activated carbon filter. It can store 7 liters of purified water. It does not need electricity. The amount of waste water to be flushed is around 2 liters every day. Pureflo UF does not have any pumps, or electrical or electronic parts, so the maintainability is higher.

Some Learning

Many sellers try to push their most expensive models that have UV as well as RO. Both technologies are not required. The RO membrane will filter out all bacteria, viruses and other living organisms. So, there is no need to kill these micro-organisms before filtering them out. Also, RO is an overkill if the water supplied has a low TDS (dissolved salts) – so you need to find out the TDS of your water supply.

Spending some time and energy to identify the most suitable combination of technologies will minimize cost, electricity usage, and wastage of water.

If you want to select an appropriate domestic water purifier in India, the site achawater.com has a wealth of information. I suggest that you use that resource to make a better choice.

Please feel free to share your views, experiences, and queries, using the “comments” feature.