Sanitation by Salt Water

Salt Water Chlorination of pools is now in increasingly common use, especially in the United States. However it is not making the same inroads into the in Europe and Australia. This article describes the water chemistry of how it works and how it compares with liquid chlorine injection that is becoming the dominantly used system outside the US.

One of the questions that we are asked most frequently is this;

“Can I have automatic salt water chlorination in my pool”

Our answer is always – Yes, But it may not be the best solution

How does Salt Water Chlorination work?

For the chemists among you this is the equation;

NaCl + 2H2O = HOCl + NaOH + 2H2

What does all that mean? – on the left side we have salt + water – and some electric current in a cell that does the nadgery bit!

On the right hand side of the chemical equation we have the HOCl that is the hypochlorous acid that kills all the germs and bacteria. However Sodium Hydroxide and Hydrogen are also produced alongside the HOCl.

The Sodium Hydroxide (or Caustic Soda as it is more commonly known) increases the Ph value of the pool water. This is why salt water chlorination must be installed with Ph measurement and adjustment system that will cater for the need to constantly measure PH and add acid to the pool water to keep it in the correct range. An overly acidic pool will eat the tiles and tile grout as well as your heat pump and be thoroughly unpleasant to swim in.

Hydrogen that is also produced is normally just lost into the atmosphere.  But oxygen can also be a side product of the cell when water molecules are split into hydrogen and oxygen there have been a few explosions in the US when the cell has been faulty and produced freak conditions.

Primary disadvantage

The primary disadvantage of salt water chlorination is that in hard water areas the cells are prone to the build-up of calcium carbonate deposits. The electronic boxes that come with the system switch the polarity of the probes in the cells to reduce this, but periodically the cell will have to be taken apart and cleaned – a thoroughly nasty little job.

In Europe a fully automatic liquid chlorine injection and Ph control system can be installed for about the same price. These systems are very reliable – but slightly more complex to set up. However they control the chlorine and Ph levels very accurately and will last as long as the pool with the replacement of a few parts.

Salt Water Pool Chlorination ; Is it a Gimmick?

There is no doubt that it automates the pool water sanitation process – but there is another more cost effective and less environmentally unfriendly way of doing it.

I suppose the main question is – what is the pool water like to swim in. Well first of all it is absolutely nothing like sea water where the salt concentration is much, much higher.

Does it feel any different?

Some people say that it is softer or silkier – I am not really into semantics like that so to tell the truth I don’t know – what I do know is that I cannot tell the difference.

Does it smell of chlorine?

The answer to this is easy – any pool filtration system that is correctly set up and running properly will not smell of chlorine.

To be honest pools where the water smells of chlorine and that turn your hair green are nearly always found to be pools that do not have automatic sanitation and Ph control systems.

No differences there then!

OK what are the other issues.

Cost of the salt

The first one is a pure cost issue – the pool will contain several hundred Euros (or Dollars) worth of salt. If it has to be emptied for any reason you lose all that salt and have to buy more. The amount of salt used is quite staggering – a 12 x 6 or 40 foot x 20 foot pool will need nearly a full pallet of salt. Part of this is constantly lost by splash-out and filtration. It is in fact a very inefficient process because all the water has to be salty and only a minute part is turned into chlorine at a time. All the rest of it just floats about in the pool.

Soakaway is needed

The second issue is what do you do with the salt water if the pool has to be emptied? It is illegal to put it into a water course or ditch because the salt will kill a great number of both plants and animals. Not only that each time that the pool is emptied there will be a progressive build up in salt concentration.

So you should have a properly designed soakaway that can be used to filter out the salt before it gets into the local streams – this will not be cheap.

Corrosive nature of the salt water

The third issue is the corrosive nature of the salt water – in most pools it will be OK – but if there is anything that will rust near your pool – the salt water could make things worse. The life of heat pumps etc will certainly be adversely affected.

Reliability of Salt Water Chlorination

The fourth issue is one of reliability. The harder the water the more often the cell has to be taken apart to be cleaned – even if the salesman says that the polarity is constantly reversed to avoid this – but they will still need to be cleaned once a year – and it’s not a pleasant job.

The fifth and maybe most important issue is that the cells only last 3 to 5 years before requiring replacement. The replacement cost will be at least 1000 Euros when labour and travelling are taken into account – and through sod’s law it will always fail at the worst time!

Supply and installation costs?

What about supply and installation costs? Well we charge about 3000 Euros for either salt water chlorination or an automatic liquid chlorine injection and Ph control system. The soakaway for the salt water can cost nearly as much again in some circumstances.

Conclusion - liquid chlorine injection is more reliable, the same cost and more environmentally friendly

The only way to absolutely guarantee that the health of anyone using a swimming pool is not impaired is to use chlorine to sanitate the pool water. Both salt water chlorination and liquid chlorine injection do the job equally well but is very difficult to see why salt water chlorination should be chosen to do the job because there is really no excuse for periodically having to empty a full swimming pool of brine into the local environment of your garden.