Pool water regulation: pH, chlorine and analysis values

The table in the regulation's annex is split into three groups: physical parameters (temperature, turbidity, colour, odour), chemical parameters (pH, free chlorine, combined chlorine, cyanuric acid, nitrate, aluminium, copper and similar items), and microbiological parameters (total colony count, Escherichia coli, Pseudomonas aeruginosa, Legionella). The table below collects the rows measured most often in practice and asked first during inspection. The exact form of a numerical limit should always be read from the annex list currently in force; cells left blank in the table are intentional.

The two narrowest rows in the table for operations are the indoor-pool free chlorine band and combined chlorine. In an indoor pool, the 1 to 1.5 mg/L range is only 0.5 mg/L wide; this band can be held only with a measuring probe and a dosing pump, not by hand-dosed chlorine tablets. If the combined chlorine limit of 0.2 mg/L is exceeded, it cannot be brought down by dosage adjustment alone; it is managed with fresh water top-up, aeration and shock chlorination.

The two values most often confused during inspection are free chlorine and combined chlorine. Free chlorine is the total of the chlorine species in the water still capable of disinfection; its main active component is hypochlorous acid. Combined chlorine, on the other hand, refers to the chloramine compounds formed when chlorine combines with nitrogenous substances such as urea coming from sweat and urine. The sum of the two is total chlorine; combined chlorine is found by subtracting free chlorine from the total chlorine measured with a field kit. The sharp smell noticed at a pool comes not from free chlorine but from chloramines.

The difference is not only in name but in disinfecting power. According to Wikipedia's chloramine article, monochloramine has roughly 0.4 percent of the biocidal effect of hypochlorous acid; in other words, combined chlorine is practically not a disinfectant. This is why the regulation sets a lower limit for free chlorine and an upper limit for combined chlorine. In a pool where total chlorine measures 1.4 mg/L and free chlorine is 1.1, combined chlorine is 0.3 mg/L, and the pool is out of limits even though it appears to be within the free chlorine band.

The link between pH and chlorine comes from the same chemistry. The acid dissociation constant, pKa, of hypochlorous acid is 7.53; around neutral pH, roughly 75 percent of the solution is hypochlorous acid and 25 percent is hypochlorite ion. As pH rises, the balance shifts toward hypochlorite, the weaker disinfectant. The regulation's upper limit of 7.8 for pH is therefore read together with the free chlorine limit: 1.0 mg/L of free chlorine measured at pH 7.8 does not do the same work as 1.0 mg/L measured at pH 7.2. The choice of pool chemicals also drives pH; sodium hypochlorite pushes the water up, trichlor tablets push it down.

The regulation sets up two separate measurement regimes. The first is the daily field measurement carried out by the operation itself: pH and free chlorine are measured every day the pool is open, during hours when usage intensity changes, and logged in the record book. The second is periodic sample analysis carried out at an accredited laboratory; microbiological parameters are tracked this way, at least once a month. The records of the two regimes are kept separately and are requested together during inspection.

In practice, the scope question resolves as follows. The regulation targets public swimming pools; hotel, apartment block, housing estate, sports facility and municipal pools fall directly within scope. A villa pool used by a single family is not subject to this permit and record-keeping regime as long as it is not opened to third-party use. But if the villa pool is rented out, opened to day-use, or turns into a shared area of a housing estate, the definition changes and all obligations come into effect. During the pool construction phase, this distinction also shapes project decisions: in a pool within scope, the sampling point, balance tank, automatic dosing and measurement probe placement are laid out from the start.

The clause to write into the specification follows directly from this table. Since the indoor pool requires a 1 to 1.5 mg/L band, an automatic measurement and dosing system is a mandatory item; the measurement probe is placed on the sample line, after the circulation pump and before the chlorine injection point. If the outdoor pool requires cyanuric acid not to exceed 100 mg/L, the mix of stabilised tablets with unstabilised sodium hypochlorite and the annual fresh water top-up rate are stated in the specification. The record-keeping obligation is also a hardware item: a control panel that logs data takes record-keeping out of the operation's discretion.

A fourth deviation relates to capacity calculation. In a heavily used pool, the contaminant load rises with the number of users; a fixed dosage setting drops below the band by the afternoon. The regulation's requirement for daily measurement exists precisely to make this deviation visible. A pool maintenance team timing its measurement to the peak usage hour is more informative than taking a single measurement at day's end.

There are three separate approaches to regulating pool water quality, and the three are not the same kind of text. Turkey's rule is a regulation; it is part of national legislation, and violating it carries an administrative penalty. Germany's DIN 19643 is a technical standard prepared for pool water treatment and disinfection; it mandates the treatment process itself before it sets a limit value. The World Health Organization's 2006 guidelines for safe recreational water environments for swimming pools and similar environments is not a binding list of limits but a guideline proposing a risk-management approach.

The common ground among the three texts comes from the chemistry of chlorine. Chlorine is more than three times as effective against Escherichia coli as bromine and more than six times as effective as iodine, and it exerts this effect through the hypochlorous acid that forms in water. The same chemistry also explains why chlorine breaks down under ultraviolet light; cyanuric acid is used in outdoor pools for exactly this reason, binding to chlorine and extending its residual life several times over. The reason the regulation sets an upper limit for cyanuric acid is that the same compound, once it accumulates too much, slows disinfection down; the stabiliser is both the solution and the limiting factor.

The current form of Turkey's regulation entered into force in 2011 and was updated by the 2013 and 2015 amendments. The text translates the framework set up by European pool water standards into the language of national inspection: a list of limit values, a measurement calendar, and a record book. For the technical team, the practical conclusion is a single one. Pool water quality is not a matter of chemical selection but of measurement and record-keeping discipline; when the right pool chemicals are combined with the wrong measurement point, a record book compliant with the regulation and a pool that is not compliant can exist at the same time.