The water that goes back into the pool

Why ranges, and not a dose

A refilled pool is measured water. SA Health, whose pool water guidance is written for pools at home, explains the reason the water has to be treated at all: water remains in a pool for long periods of time, so it must be treated to keep it clean and safe, and proper disinfection and filtration of pool water kills harmful microorganisms and removes body fats, oils, soil and other contaminants.

What the same page gives is a set of ranges to hold, and a routine for checking them. It gives no dose, and none is given: a dose is an instruction for one pool’s volume and one product’s strength, and the ranges are what a reader can act on without a measurement of their own pool.

The ranges, as SA Health gives them

Free residual chlorine

If chlorine is used, the free residual chlorine concentration in your pool should be maintained at 1.0 to 3.0 mg/L. The ideal level is 2 mg/L.

pH

To ensure chlorine works efficiently, the pH range must be maintained within 7.2 to 7.6, which the page also gives as the ideal pH of water for the comfort of pool users.

Stabiliser

To prevent chlorine from rapidly breaking down in pools exposed to direct sunlight, cyanuric acid can be added to reduce the amount of chlorine consumed, and it should be maintained at a level of at least 30 mg/L and no more than 50 mg/L.

Total alkalinity

Total alkalinity should be maintained in the range of 60 to 200 mg/L and adjusted as necessary by using sodium bicarbonate as advised by a swimming pool supplier, and it should be checked at least once a week to prevent cloudy water, scale formation and metal corrosion.

Calcium hardness

The ideal range of calcium hardness is 150 to 400 mg/L, checked once a week to prevent scale formation.

One more line belongs with the ranges, and it is about the water itself rather than the chemistry: only treated mains water from a domestic water supply should be used to fill a pool, and an owner who wants to use another water source should seek advice from an environmental health officer at the local council.

The testing routine

The routine is as published as the ranges are. It is important to test the water before use and at least once every day for pH and chlorine or other disinfectant concentration, other parameters should be measured at least weekly, and reliable pool water test kits should be used, with kits available from swimming pool shops, some supermarkets, hardware and major department stores. Heavy use changes the timetable rather than the range: more frequent testing should be done in hot sunny weather or when the pool is being used by many people, so that changes in water quality are detected before problems develop.

Victoria writes the same habit with a reason attached. The Better Health Channel puts pH and chlorine on a daily check, with the best moment being before the first swim, so that any change in the water overnight is caught, and it says a pool needs checking regularly if the water is to stay safe to swim in.

The smell that means the opposite

One result of testing surprises people, and the Better Health Channel in Victoria writes it down. A strong smell of chlorine can irritate the eyes, the nose and the skin, and the cause is the opposite of what most people assume: it is too little chlorine rather than too much, because chloramine compounds form when the chlorine is low, and it is those compounds that carry the smell and do the irritating. A pool that smells strongly is asking for its chlorine level to be checked, and it may need more chlorine rather than less.

There is also a point past the routine where the water needs more than a range. SA Health says that after a pool is heavily used, after a rainstorm, or if a pool has been poorly maintained, it may require shock dosing to bring it back to a safe standard for use. What a shock dose is for one pool is not given; the page that names the practice is linked below, and its own instructions are where the numbers belong.

Topping up, and the two waters after it

A refill is rarely one event. SA Health asks the owner to top the pool up regularly using a hand-held hose or bucket, to add all top up water via the skimmer box with the filtration system running, and to check disinfectant and pH levels after topping up. Icon Water adds advice for ACT pool owners: overfilling a pool stops the filter working properly and sends water over the edge.

And before any of it, in Sydney Water’s area, the water going out is already a permission: Sydney Water asks that the Water Wise Guidelines be checked before any water is removed, to see whether refilling the pool needs a permit, and a permit is approved only where the drain and the refill cannot be avoided. The discharge guide sets that rule beside the other states’ disposal rules, which is where it belongs.

A spa’s water can be partly replaced

Queensland Health’s private spa guide offers an option: alternatively, you can replace at least one quarter of the water in your spa pool monthly, and cover the spa pool when not in use to prevent leaves, dust, pollen and insects, as well as animal and bird faeces, from contaminating the water. The same guide sets a testing rhythm for the spa: disinfectant levels should be tested prior to use and at least three times a week. And one line in it belongs to the shock process rather than to the spa: the cover should not be placed over the spa pool during the shock dosing process.

What the refill asks

Read together, these sources give the refill one shape: SA Health asks for treated mains water, top-ups through the skimmer with the pump running and a check after every top up; hold the five ranges above with the source each comes from, test as often as the source for your pool asks (SA Health: daily; Queensland Health’s private spa guide: at least three times a week), and, in the Better Health Channel’s words, check the chlorine when the pool smells strongly, as it may need more. Where the water came from, and where it goes next time, is the draining guide’s subject; what the finished barrier around it must answer is the inspection guide’s.