How to Safely Filter Water for Drinking

Water is the substance of life, but do we take it for granted. Have we squandered it and abused it too much. How can we acquire a more natural supply of water for everyday and in times of emergency?

How to Safely Filter Water for Drinking
Photo by Pablo Molina / Unsplash

Drinking water is so important to life, but many of us do not think about it. It comes out of our taps, is already "safe" to drink and we unashamedly consume it and waste it.

Should we treat water in this way? Is it worth a second thought?

It has been suggested that contamination of the water supply would be the most effective way to kill a large number of Westerners (Americans and Europeans). There may come a day when we no longer want to consume the water from our taps and that day may be sooner than you care to imagine.

What is in the municipal water supply

Filtration ponds
Photo by Ivan Bandura / Unsplash

The municipal water supply goes through a three step process.

  • Primary filtration removes the solids
  • Secondary filtration introduces chemicals to help with removal of fine solids
  • Tertiary filtration is the removal of pathogens

All the water that comes out of our taps, has generally gone through the above steps. All the water from streams, rivers, reservoirs and waste water from our drains arrives at a water treatment facility.

Primary filtration of the water has it go through a series of filters, just like other filters that you'd be familiar with, such as those in your vacuum cleaner, pool pump, fish tank, or air-conditioning. These filters have varying sizes of mesh to filter out different size solids.

Some chemicals may be added already at this stage to soften the water (remove minerals) and to kill pathogens. These chemicals include Sodium Carbonate and Chlorine.

Secondary filtration introduces more chemicals to make the fine particles clump together in processes known as coagulation and flocculation. These particles are then easier to filter out. The chemicals added may be Aluminium Sulphate or Iron. Other chemicals may be added to raise or lower the pH of the water to neutralize it or again to change the hardness of the water.

Tertiary filtration adds further chemicals to kill pathogens. The most common chemical added is Chlorine. Ozone may also be used.

In some countries or states Flouride is added to the water to counteract the harm to teeth caused by consuming too much sugar and not brushing properly. Talk about treating the symptom and not the cause!

Why we want to filter our water

The filtration process carried out by our municipality is primarily concerned with the removal of solids and pathogens. There are however, other chemicals and contaminants that we may find in our drinking water.

Lead is one highly publicized toxic chemical that is not safe at any level in our blood supply. It has been causally linked to learning disorders, lower I.Q. and even crime. Lead usually enters the water supply after the filtration process as it was formerly used in pipes.

Astrazine and Nitrates are common fertilizers and these are commonly detected in drinking water. They enter the water supply by run-off from agricultural land, and then they are not effectively removed through the municipal filtration process.

Pharmaceuticals enter the water supply either through urine or by being flushed down the toilet. They are also not effectively filtered out and so are commonly detected in the drinking water.

Other chemicals or hazards include radioactive contaminants, chlorine by-products, arsenic, mercury, MTBE, micro-plastics and the list goes on.

Even though the water is filtered and treated following strict guidelines, our good-health is often not the government's primary concern. To ensure good-health for ourselves requires us to take our health into our own hands. That is why we should consider the filtering even the water that comes from our taps.

What types of filtration should I consider

Carbon filtration is the simplest and most obvious first choice of filter. These filters are available from every store and are perfect for every day use without too much trouble.

Brita Water Filter

For less than 20 Euros, Dollars or Pounds, this is an obvious first choice for filtering water.

Purchase from Amazon

Cartridge-style carbon water filters such as these need to have the filter replaced regularly, they tell you monthly, I do it every two months. The reason for the regular change is that channels can form within the cartridge, these are small pathways that the water will always follow because there is less resistance. It means that the water is less filtered than with a newer filter. The other reason for replacing the filters is that the contaminants can accumulate thereby also making the filtration less effective.

The carbon filters claim to remove chlorine, lead, copper and mercury. In the US there is a new version of the Brita filter available that does not rely on carbon granules and so can last up to 6-months yet still remove the same chemicals.  

Carbon filtration is available in various other guises. There is the  faucet, or tap-connected filter where the filter is attached via some plumbing under the basin. This is a more expensive option not just in terms of the plumbing but the filters themselves are less common and therefore priced less competitively.

Then there are variations on this theme, different styles of cartridge, different filtration media etc.,

The Big Berkey

Berkey filters deserve a special mention because anyone who has paid attention to survival blogs for more than a few minutes will have come across these exceptional filters.

The filter cartridges are washable and can last for up to 10 years, but at close to 150€, they still average out at 15€ per year. The advantage however is that the filtration offered is some of the best available. This device is able to filter our metals, pathogens, some pesticides, fertilizers and other chemicals. If your water has flouride in it then you need to purchase the additional flouride filter and that needs replacing yearly.

The Berkey can be safely used to filter totally unpurified water from streams, wells or rainwater and requires no electricity to operate.

Although I don't own one yet, I am seriously considering buying one.

Reverse Osmosis

Reverse osmosis is a process that I first became aware of whilst working in the submarine industry. It can be used to purify either dirty water, or be used to desalinate sea water. It can remove all contaminants and pathogens.

The problem with reverse osmosis is that it requires a lot of energy to run the systems and it usually removes all the minerals from the water which are beneficial for good-health.

Furthermore, in order to protect the membranes used for reverse osmosis, a filter is used, similar to the filters mentioned above, and these need replacing regularly.

Distilled Water

Distillation is the process of separating fluids by use of their varying boiling points. This is the process used to separate alcohol from water to produce the high concentration liquors like whisky, brandy and gin. It is also the process used to separate the chemicals in crude oil to produce the different gasoline fuels and the multitude of plastics.

Boiling water will kill most pathogens but it will not remove the chemical contaminants and metals. By causing the water to turn to steam and then condensing the steam in another container you will have transferred only the water (and chemicals with a lower boiling point). To avoid transfer of other chemicals then you could keep the temperature below boiling point. Anything that condenses in the container below 100℃ can be disposed of, and then a new container used to capture the water which will be transferred at exactly 100℃.

The disadvantage of distilled water is that no beneficial minerals will be in the water. It is generally not considered a good long term solution.

The advantage is that once you own a suitable still, it can be used on a campfire or with bottled gas and it can be used to make alcohol for sale or consumption.

Image of basic countertop still

Can we safely drink rain or spring water

Very simply, yes you can drink rain or spring water. The caveat is that it depends on what happened to the water before. Mountain springs are going to be cleaner than those found in the countryside around a town, because farming pollutants will likely enter the water supply. Cracked pipes from household and industry waste may also lead to contamination. So the more remote the water source the better.

Legally, most countries and states have laws prohibiting the building of property without a connection to the municipal water supply. This can be a problem for those seeking an off-grid lifestyle but is very much country and state dependent.

If you live in a temperate or tropical climate with regular rainfall then collecting rainwater is a brilliant way to meet your water needs. The less rain water you get, the larger the storage facility you will need. You should include some pre-filtering that can be as simple as a grate followed by an old pair of tights. Keep the lid and filter tightly fitting to avoid the chance of any animals falling in and drowning.

It is also worth bearing in mind that with increased burning of fossil fuels and the evaporation of other agricultural chemicals can lead to pollutants being found in rain water. Recently in Europe sand from the Sahara blew over from Africa and every surface was covered in fine sand particles. Filtration will ensure the removal of particles and other pollutants.

Chlorine Granules for Water Purification

Available from most hardware stores, these can quickly purify a large amount of water making it safe for drinking.

Purchase Chlorine from Amazon

How can I purify water in an emergency

By adding a small amount of chlorine to water, you can eliminate most pathogens. If you purchase pool chlorine then it can last for many years and is cheap to purchase. You can also use household bleach. We have a small 2000 litre (500 gallon) pool and 1 teaspoon of chlorine will purify it for about 1 week. With household bleach you'd be looking at a teaspoon for every 10 gallons (read the EPA guidance here).

Boiling water is always the go to answer if you have sufficient fuel. Ensure you have a nearby supply of wood and a suitable container for boiling the water, either a camping kettle, or a cast-iron sauce pan is best.

You can also rig up a solar still that works with the sun to evaporate water and collect it again. The principle is simple but you need a few supplies and some clear thinking.

A solar still uses the sun to heat up and evaporate the water so the sun should be able to see the water, but in a squeeze a tarpaulin or tent fabric would work (something waterproof). There must be a large flat container for the unpurified water and a smaller but taller container for the purified water. You stretch the fabric over something, some sticks stuck in soft ground would be ideal, and then place a stone or other weight in the middle of the fabric to weigh it down just above the taller container. In this way the condensation will gather on the fabric and run down to the stone at which point it will form drops and drip down into the tall container.

In the absence of water and other supplies then an even more basic still can be assembled by digging a hole into the ground, placing green foliage around a container and laying a polythene sheet (or plastic bag) over the top, keeping it in place with soil or stones. Place a stone in the middle of the sheet for the condensation to run to. The foliage in this case is the source of water.

How can I safely filter water long term

Now for the longer term, and possibly as a permanent solution, if allowable by building regulations, is to establish your own filtration system.

We have looked at the large scale municipal water treatment facilities, and we have looked at small scale jug-sized water treatment. They share the same principles, varying sizes of filters that the water passes through to filter our particles plus the addition of chemicals to remove pathogens. This exact same principle works at household scale, only the quantities of filtration substrate and the size of the containers change. It is up to you how many individual steps you want.

The main components are as follows:

  • Large particle filtration - grate or grill to keep out stones, leaves and animals
  • Medium particle filtration - something like an old pair of tights or some cheese cloth at the bottom of the down spout. You can then wash it as and when required
  • Water baffle - to prevent fast flowing water from disturbing the sand layers
  • Biosand or activated charcoal
  • Fine sand - performs bulk of the filtration
  • Course sand - offers structural support to the fine sand above
  • Gravel - offers structural support to the sand above and allows water to flow out of the tube

OHorizons, CC BY 3.0, via Wikimedia Commons

This can all be adequately done in one 100 litre drum, but it can also be done with individual drums, each one performing a different part of the filtration. Or it can be done by stacking smaller containers on top of each other, such as food grade 5-20 litre buckets.

Building regulations

If this system needs to satisfy building regulations but you want to remain off-grid, then absolutely keep in close contact with the local housing department to see what is possible, the most likely acceptable system would be a multi-step cartridge filter system possibly including a chemical doping system.

The Earthship water system is recommended for long term rainwater filtration systems and further information on it can be found here: Catch water - potable drinking water - Earthship Biotecture


I hope this article has sparked some thoughts in your mind about the water that we drink and how it arrives at our homes. Much more could be written including on the health benefits of certain types of waters versus the possible problems caused by contaminants.

Also in the future I hope to cover more details about how to practically build such a system for off-grid living. Perhaps I'll also feature a review of the Berkey water filter.

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