Clear Clean Water

tiled polyblok pool with light features and ceiling windows

I. Our Water Quality Guarantee

Bluepools is totally commited to ensuring that every one of its pools is equipped to provide the best water quality possible. Every pool should be full of Clear Clean Water that makes the owner proud of their facility with everyone is eager to swim.

When a pool's water is lifeless, smells of chlorine and is murky, no one wants to use it and the pool becomes an expensive "white elephant". If the Bluepools Principles (described below) have been followed, the pool will always be full of water that really does sparkle.

But if your pool has not been designed in accordance to these principles it will not be easy to undertake the necessary remedial works. You may have to replace all the buried pipework and any new equipment such as water inlets and skimmers will have to be cut into the pool walls.

II. How we achieve Clear Clean Water

There are five fundamental design principles that need to be followed to produce "Clear Clean Water" in a swimming pool and many pool installers ignore them in order to save money on the cost of the pool equipment.

The Bluepools Principles

  1. Every single litre of water in the pool needs to pass through the swimming pool filter 4 times a day.
  2. The filter needs to be large enough to keep the velocity of water passing through the filter down to 30 metres per hour.
  3. The pool filtration pump should be sized precisely to pump the entire pool water volume through the filter 4 times per day.
  4. The water must circulate through an Ultra Violet cell that kills the pathogens in the pool water by passing the water in front of an ultra violet light with a wavelength of 253.7 nm.
  5. The pH level and active chlorine content must be continuously tested then treated by pumping the precise amounts of dilute hydrochloric acid and liquid sodium hypochlorite required to maintain the pH at 7.0 - 7.2 and active chlorine content at 0.8 - 1.0 parts per million.

III. Why these principles work:

The exact number and precise location of inlets and skimmers must be planned with great care to ensure that all the water in the pool corners is pumped through the filter thus ensuring that stagnant water does not result in turbidity (Turbidity is a measure of the degree to which the water loses its transparency due to the presence of suspended particulates).

Pumping the entire pool volume through the filter 4x per day is the generally accepted pool industry standard required for better water quality.

Vertical water circulation is also needed to generate vertical water movement in the pool through the pool floor outlets. Two of these are always necessary to make absolutely sure that nobody can be trapped down onto an outlet by the suction from the pool pump.

The faster the water flows through the sand in the filter the less effective the filtration is - many domestic pools have filtration rates that are far too high (50 m / hour is the norm) because the filters are too small.

An unnecessarily powerful pump will increase the flow rate through the filter (see Principle 2) and cost more to run.

Over the past 50 years, many efforts have been made to replace chlorine in swimming pools but none have proved to be satisfactory until recently.

Ultraviolet radiation of a particular wavelength (UV-C – 253.7nm) has a very strong biocidal effect when used to treat water. It renders micro-organisms in the water harmless, particularly those that are unaffected by chlorine. UV-C light is the most damaging part of sunlight that doesn't reach the earth, so a special electric lamp is needed to generate this radiation.

This means that in swimming pools, UV is an extremely powerful disinfectant. It is even effective against Cryptosporidium Parvum and Giardia Lamblia, for example. These are particularly nasty micro-organisms that can survive in a swimming pool despite the use of chlorine.

In addition to its biocidal action, UV has an extremely strong oxidising effect which means it successfully removes organic pollution from the pool water. When chlorine is used in conjunction with Ozone or UV the harmfull chloramines that can for instance cause eye/skin irritations are destroyed.

With UV purifying, nothing is added to the water to prevent any new infections. In other words, although the water passing through the UV-C is disinfected it does not create disinfectant that will eliminate pathogens in the pool water. The water from the UV purifier returns to the pool and will typically remain there for up to 4 hours until it is treated again. So, any pathogens instantaneously introduced by bathers in the pool would not be treated until that water arrives back at the UV treatment unit in four hours’ time. This presents a small but significant risk of causing sickness to bathers - see Principle 5 below.

UV Cell Disinfection

To ensure that pool users do not transmit pathogens to the pool water it is always necessary to maintain a small residual concentration of a secondary disinfectant (such as chlorine) in the pool. For public pools in most countries, this is in any case a requirement imposed by the regulatory public health authorities. The addition of a secondary disinfectant ensures that the water itself acts as a disinfectant. In outdoor pools this residual disinfectant is also required to stop the formation of algae when the pool water temperature rises.

Although the use of UV does not remove the need for a secondary residual disinfectant like chlorine, it's total concentration in the pool water can usually be significantly reduced (in public pools to the minimum legally allowable concentration).

The effectiveness of chlorine disinfection when it is added to water is maximised when the water is neither acidic or alkaline. In the UK water is predominantly alkaline and needs the addition of dilute acid to obtain the required neutrality. Bluepools uses a system that continually tests the water and adds small doses of weak acid to ensure that the water is always neutral. The Bluepools system also tests the actual active chlorine content and injects exactly the right amount into the neutralised water in order to achieve a tightly controlled chlorine content.

Tap Water has an active chlorine content up to 0.8 parts per million and hence the Bluepools system that is designed to provide the same chlorine content will be indistinguishable from tap water.

Automatic Chlorine Injection

Every Bluepools pool is provided with the pool equipment that complies with these 5 Principles.

The Clear Clean Water that it provides has the same chlorine content as tap water.

IV. Salt Water Chlorination:

We have not mentioned salt water chlorination and we often get questions about it. In summary it is a very crude method of water disinfection that was originally invented to facilitate advertising that pretended that there was no chlorine in the water and to reduce the amount of pool maintenance for American pool owners.

The salt water concentration in the pool water is achieved by using 2.5kg of salt per cubic metre of water (about 150 kg in a 50 square metre pool) which results in a salt concentration of about 2500 parts per million (2500 ppm). The concentration of salt in sea water is about 15 x higher and so the water in salt water pools does not taste like seawater and moreover is pure Sodium Chloride and not a very large mixture of myriad types of natural salts.

In a salt water pool the water is pumped through the same type of filter as in a normal pool and then passes through a cell with two electrodes. When a current is passed between the electrodes through the salt water, the salt is turned into active chlorine at a concentration of 3 - 4 ppm.

The primary drawbacks of these systems are as follows:

As a result, all salt water pools should incorporate automatic pH measurement and dosing but even this will not reduce the total alkalinity that can only be reduced by continually diluting the pool by dumping the water and replacing it.

There is simply no doubt whatsover that salt water pools may be ok in the western US where the water is soft but in the hard water prevalent in the UK it is not suitable for use in any swimming pool.

For more details on Salt Water Chlorination.

V. What will all this cost?

The capital cost of a "Clear Clean Water" system for a 50 square metre pool will be around £2500 + VAT with an annual operating cost of about £15 per week.

Salt water systems including automatic pH measurement and dosing will cost about the same amounts.

Bluepools has a large UK portfolio of very successful pool projects that were all custom engineered to meet a wide range of design challenges.

Our solutions are illustrated here: