Buying A Water Filter

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Water & Water Filters: An Interview With Ken Digby by Jane Thurnell-Read

Many people are concerned about the quality of the water that comes out of the tap/faucet, so I decided to ask Ken Digby of NT Laboratories (UK) to talk to me about this whole issue. What are the different types of water filters? Is a water filter necessary? Here’s our conversation:

Should people be concerned about the quality of their drinking water?

This is a really difficult question. Water authorities have to meet certain safety standards, so in technical terms you don’t need a water filter system, but personally I feel that most people would benefit. The water boards also do tests for colour and taste, but this is very subjective – notice how these will vary in different parts of the country – and still meet the standards.

What about chlorine?

Most water authorities don’t use it routinely, but if they do emergency repairs to the piping, they will put a bag of chlorine into the system. The consumer won’t know it’s been done. But hotels have to use chlorinated water that comes from a storage tank – that’s why you’ll see a notice in hotel’s that the water in the rooms is not safe to drink – the chlorine levels are too high. In other countries, such as the USA, water is routinely chlorinated, but many apartment blocks come with a water filter system already installed.

Apart from taste, smell and chlorine, what might people be concerned about?

In cities supplied with water from rivers the water may be put back in and taken out again several times along its length, so there can be hormones from the contraceptive pill, and organic solvents from industrial processes. Pesticides and fertilizers, as run-off from farm land, can also be found in drinking water.

In some areas of the UK, for instance, nitrate levels in drinking water exceed WHO safety levels.

Heavy metals, such as aluminium, zinc and lead, are only really a problem in soft water areas because they can dissolve into the water. Water authorities may say that the levels are so low they are not a problem.

Aluminium sulphate is sometimes added to the water supply to remove particles from the water.  The levels of aluminium are very low, but accidents can happen as they did in Cornwall (UK) a few years ago. Many people were seriously affected by this catastrophe.  Normally most of the aluminium sulphate will be removed as it combines with the particles and falls out of the water as sediment.

Trihalomethanes can also be present in the water – formed in small amounts when chlorine and natural organic matter in the water interact. Chloroform is a trihalomethane, these substances have been associated with cancers and allergies.

In some areas peat will be suspended in the water. This is probably not a health hazard, but it can affect the taste and colour of the water.

What about problems with the materials in the water pipes?

Water pipes used to be made from galvanised zinc – iron coated with zinc; these pipes can break down over many years, releasing zinc into the water supply. In some areas you’ll also have rust coming off the pipes.

Some old pipes in the UK that run under farmland are made from asbestos. Sometimes farm machinery will damage a part of the pipe, so the water board will cut that piece out and replace it with a piece of new plastic pipe but leave the rest of the old asbestos pipe in place.

Modern pipes are mainly made from polythene, and though some people are concerned about phthalates leaching from the plastic, I don’t really think it’s a problem.

So, should people use a water filter?

Water authorities have to operate to certain legal standards, and they will often say that the levels of certain chemicals are below the limits set by WHO, but nevertheless a lot of people feel healthier if they use filtered water.

I’ve found that children with eczema often benefit from filtered water, particularly if they are using filtered water to shower or bath in. If you have a child with eczema, you will often know when it is time to change the filter, because the child’s eczema will come back!

In the UK the water company has to give you an analysis of your water if you ask for it. It will only be a typical analysis for your area, rather than being your particular water. I’m happy to look at them for people, if they want help interpreting the results.

There are lots of different types of filters how do I choose one?

Most filters use carbon to remove hormones, pesticides and solvents.

The jug-type filters are made from granular activated carbon. This is a bit like putting carbon granules in a tea bag and letting the water flow through. It will do something but it’s not the most efficient. It contains a resin which is good at removing calcium carbonate – this is found in hard water areas and gives the ‘scum’ on top of your cup of tea.

Filters with a carbon block are better. The carbon is powdered and then reconstructed into a solid block. This is more efficient than the granulated filter because the particles are very small so there is more surface area for the water to come into contact with. You can use this system to filter all the water in your house, not just the drinking water. They will remove hormones, pesticides, organic solvents and nitrates. Some are impregnated with other materials and so will also remove heavy metals.

Some sophisticated filters have ceramics, carbon block and resins. The carbon block does 99.9% of what you want apart from scale removal in very hard water, so you might want to add a descaler for your tap water.

Some carbons have silver added to them to prevent the growth of bacteria and algae.  This is good when the filter is only going to be used intermittently with many days or weeks in between uses.

What about reverse osmosis water filters. To me water from one of these seems like ‘dead’ water. What do you think?

Reverse osmosis involves forcing water through a very fine membrane under pressure. It removes everything dissolved in the water, so you get very pure water. Normally they come with a pressurised reservoir that water drips into. The reservoir connects to a little tap, and will give you 4-8 gallons [18-36 litres] of water a day, with 24-48 gallons [108-216 litres] of waste water.   In general you need a carbon filter as well, otherwise too much organic material will get through and contaminate the RO membrane. This will be a breeding ground for bacteria. This is also why RO systems need to left running all the time. If you stop the process, the membrane becomes contaminated. In general you need to change the membrane once a year.

RO filters remove nutritional salts – such as calcium and magnesium salts –  that are dissolved in the water. These are left in by carbon filters.

What about fluoride?

Carbon filters do not remove fluoride. In England the only place that is routinely fluoridated is Birmingham. In Scotland there are naturally high levels of fluoride in the water. The main way to get rid of fluoride at the moment is using an RO filter.


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