Saltwater or Freshwater Pool?

The honest pool comparison for the Algarve. Hard water, a lot of chemistry, and the eternal question of where the old water should go: we look at both systems without a sales pitch — with tables, charts, and honest pros and cons for the private pool in the Algarve.

01  —  THE UNDERLYING PROBLEM

The Real Problem: Water in the Algarve

Before debating salt versus chlorine, it's worth looking at what actually comes out of the tap, the cistern, or your own borehole. Large parts of the Algarve — especially the Sotavento between Loulé and the Spanish border, but also many inland areas — sit on limestone bedrock. Groundwater passes through this rock and picks up large amounts of calcium and magnesium along the way. The result: water that, in many zones, is well above 400 mg/l calcium carbonate — the threshold beyond which cloudiness, limescale deposits, and clogged filters, pipes, and heat exchangers become part of everyday life.

Rough reference values for orientation, not an official measurement series. The Sotavento algarvio, because of its limestone soils, is regularly considered one of the hardest water zones in Portugal.

This hardness shows up directly in pool maintenance: alongside the actual disinfectant, pools in the Algarve often also need anti-limescale products, pH-minus — hard water tends to push the pH upward — and flocculants. A cocktail that costs time, money, and storage space in the plant room.

This is exactly the point where the suggestion almost automatically comes up: "Why don't we just install a salt electrolysis system?" The two main arguments you hear from pool technicians are almost always the same: a noticeably softer, more pleasant feel to the water — and fewer limescale problems.

02  —  THE TECHNOLOGY

How Does the Salt Actually Get Into the Pool?

"Saltwater pool" sounds like a single technology, but it's actually an umbrella term for several, sometimes very different systems. The overview below shows what's really behind the common terms.

Simplified cycle: dissolved pool salt is split in the cell by electrolysis into chlorine gas, which immediately reacts to form hypochlorous acid (HOCl) and flows back into the pool via the filter circuit.

03  —  THE MISCONCEPTION

But: Saltwater Also Needs to Be Disinfected

This is probably the most misunderstood point in the entire saltwater debate: salt itself disinfects nothing at all. It is merely the raw material from which the system continuously produces chlorine. Anyone with a saltwater pool is therefore still swimming in chlorinated water — the chlorine is just no longer poured in from a canister, but produced by the system itself. Marketing claims like "100% chlorine-free" are simply inaccurate for pure salt electrolysis.

04  —  THE AUTUMN CLASSIC

Where Does the "Old" Water Go?

At the latest when it comes to the autumn backwash or fully draining the pool before a renovation, the question comes up that's regularly debated heatedly in Algarve forums: where should the water go? Three options are common in practice — with very different consequences.

Soakaway / Septic Tank (Fossa Séptica)

Most quintas and montes in the Algarve hinterland — including many away from the coastal towns — aren't connected to the public sewer network but to a fossa séptica or a mini-ETAR (small treatment plant). Large amounts of pool water all at once are not a good idea here: both residual chlorine and the salt load, unusual compared to normal wastewater, can temporarily throw the bacterial culture in the tank off balance. In small, spread-out amounts — such as during normal sand filter backwashing — this is usually unproblematic in practice. A complete drain of 30–80 m³ all at once, however, is not.

Public Treatment Plant (ETAR)

Where a connection to the public sewer network exists — usually in town centres and newer residential areas, less often for standalone properties inland — discharging into the wastewater network is the simplest solution: the ETAR is designed for strongly fluctuating inflow values and dilutes chlorine and salt residues without any problem. For larger volumes, it's worth making a quick call beforehand to the relevant Câmara Municipal or to Águas do Algarve to check whether registration is required — for the average private pool, this is usually just a formality.

"Simply" Into the Garden

The most pragmatic — and most common — solution in the Algarve. To avoid this becoming a problem for the soil and plants, a few basic rules apply: let residual chlorine break down in the sun for 24–48 hours (UV light reliably decomposes free chlorine), spread the water over as large an area as possible rather than releasing it in one concentrated spot, and favour salt-tolerant plants. Olive trees, for instance, tolerate occasional salt exposure well; sensitive neighbours such as young citrus trees or rose beds should generally be avoided. A permanent pipe into an open watercourse or drainage channel always requires a permit — for larger or commercial pools, this falls under the responsibility of the relevant water authority (APA). For a normal private garden pool, occasional, spread-out draining is widespread practice and generally uncritical; when in doubt, it's still worth a quick check of your local Câmara's regulations.

05  —  THE FULL PICTURE

Salt vs. Fresh: Pros and Cons at a Glance

06  —  THE FAMILY QUESTION

And What About the Children?

For many families, this exact point tips the scales: children often react more sensitively to chlorine smell and red eyes than adults do. Saltwater is therefore often marketed as the more child-friendly choice — and indeed, a pool's salt content is around a tenth of seawater's, so the occasional mouthful while playing is harmless.

The more honest message: the decisive factor for red eyes and skin irritation is the same in both systems — a stable pH between 7.2 and 7.6, and as few chloramines as possible, which are the actual cause of the typical "chlorine smell". A well-run classic chlorine pool can be just as pleasant for children's skin as a poorly balanced saltwater pool can be unpleasant. Anyone swimming with children often should therefore — regardless of the system chosen — test more rather than less often, and keep an eye on residual chlorine and chloramines, rather than relying solely on the "saltwater" label.

07  —  CONCLUSION

For Environmentally Conscious Pool Owners: Freshwater with Grander Revitalisation, Without the Old Problems

Anyone who, while reading this, was thinking mainly about their own soil and the neighbouring garden can't get around one point: salt that's once in the pool doesn't simply disappear on its own. Every drop that ends up in the garden leaves behind a small salt load, which can add up over the years if you don't consciously counteract it.

Anyone unwilling to accept this trade-off ends up almost inevitably back with the classic freshwater pool — but doesn't have to return to the old heavy-handed chemical approach to do so.

In practice, the most coherent combination for an environmentally conscious yet uncomplicated Algarve pool is usually: Grander water revitalisation, low-dosed chlorine as reliable residual protection, complemented by UV-C or ozone to reduce chlorine demand and chloramines, plus consistent pH and filter care. This resolves the entire water problem of the Algarve described at the outset — without the salt load that, in the end, you'd find again in your own garden.