Reverse Osmosis Swimming Pool Water Purification

Swimming Pool Water Purification with Reverse Osmosis - Playing with Fire

Sanitizing your vanishing, negative or infinity edge swimming pool or spa with a Reverse Osmosis filtration system can have potentially devastating effects on any product that contains cement, minerals or metals.

Understand Water Chemistry

People who market "gimmicks" to the swimming pool industry, oftentimes come from other industries.  They have a "brainstorm" about how they might enlarge their markets, and enter new markets without "doing their homework."

The manufacturers of Reverse Osmosis filtration systems who market to the swimming pool industry and pool owners, simply did not understand the complex dynamics of swimming pool water chemistry. 

It's all about "the Balance"

Swimming pool water needs to be maintained in a complex balance of sanitizers, pH, alkalinity, and minerals.  If any of these get out of balance with the others, the water will seek to create it's own balance.

Potential damage to cements, thinsets, grouts or plaster can easily occur, even though the water chemistry readings appear normal.

It's Got to Come from Somewhere

Let's assume that a new pool had the water balanced prior to a Reverse Osmosis system being activated.  The water contained 300 parts per million (ppm) of calcium.

When the Reverse Osmosis system is brought on-line, it immediately attempts to remove EVERYTHING from the water.  This includes anything dissolved in the water: sanitizer (chlorine/bromine), minerals, metals, calcium...

Eventually, the calcium level drops in the pool water to the equilibrium point.  At this point, if the calcium level drops any lower, the water will begin to seek alternative sources of calcium to maintain that equilibrium.

So, begins the degradation of any material in constant contact with the water that contains calcium, minerals or metals.  Testing the water will indicate that the levels are okay.  What the test cannot and does not indicate, is the SOURCE of the calcium, minerals or metals.

As make up water is introduced to the pool from the fill line, alternative minerals are introduced.  These may be drawn out of the make-up water & into the plaster.  The plaster is attempting to re-balance itself with alternative minerals... and the plaster begins to degrade.  The plaster may begin to stain, soften, crumble or dust.

Metallic objects in contact with the water may also be "attacked" by this imbalance. The copper within the pool heater, heat pump or solar panels may begin to corrode.  The soft copper is easily attacked by aggressive water.  These components will begin to get thinner & thinner until they begin to leak.  This is why R.O. systems within a house are plumbed with only plastic tubing... the R.O. treated water will actually eat copper lines.

Issue caused by the Builder/Specifier

The responsibility of any resulting damage belongs to the pool builder or party that specified or installed the Reverse Osmosis Purification System.  A pool service company has no means to verify the source of balancing components of the pool water.  It simply is not a "service company" problem.

These units are installed as a side-stream purification system.  They work in parallel with the primary filtration system.  So, they are removing minerals from the water faster that the minerals are being replaced.  Eventually the equilibrium point is reached & the water begins to extract minerals from any alternative source it can.

NO TEST exists that can determine the SOURCE of the minerals present in the water, so the damage continues unchecked... until visible damage has already occurred.   The first sign is usually mineral staining or crumbling grout.

If the system only treated the fill (make-up) water, then the dilution of the pool water may never reach the equilibrium point.  This is because as water evaporates, the minerals are left behind.  The mineral concentration increases from evaporation, while the R.O. treated water with zero minerals, dilutes the remaining water.  This is not to say that the equilibrium point would never be reached.  It all depends on how fast the minerals concentrated & how fast they were removed.

But, because the R.O. system is only treating the make-up water and not treating the entire pool when ever the filtration system is running, the calcium levels tend to stay high.

This same situation can occur by installing a water softener on the make-up water line.  In areas with extremely high mineral levels in the drinking water, a water softener on the fill line will help keep the pool water from becoming so hard that calcium deposits develop everywhere (hard water spots or a line on the waterline tiles).

Don't buy into a program because of a company or salesman's pitch.  A builder or specifier needs to understand how the system works, how it effects the water chemistry and any potential detrimental effects it may cause to the project.

One way to enjoy Reverse Osmosis water

The only way to safely enjoy reverse osmosis water in your swimming pool... is to drink a glass of it while floating in the pool.

It is virtually impossible to create a pool that does not contain SOME metal components.  Even a vinyl liner pool with plastic pipes & pumps would contain metal in the heaters, fixture screws, handrails and pump shaft seals - there is going to be metal in contact with the water.  And water without ANY MINERALS is like a giant wild hog... constantly looking for something to eat.  And it will not stop until is is satisfied...

R.O. systems utilized for drinking water in a household are fabricated with plastic tubing, fittings and ceramic faucet seals.  No metal is in contact with the R.O. water until it actually passes through the faucet spout... the last 3-4 inches before entering your glass (not long enough to dissolve the faucet).

You sold it... you own it!  

Any damages cause by this type of equipment is the responsibility of the builder/specifier and manufacturer.  The pool builder/specifier will need to repair any resulting damages and the manufacturer will be financially liable for those repairs.


Paolo Benedetti - Aquatic Artist
"Creating water as art."™
Aquatic Technology Pool & Spa
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