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Using Rainwater to Top Up Your Swimming Pool

Using Rainwater to top up your Swimming PoolRooftops gather an amazing amount of water when it rains, yet most of this simply goes to waste as stormwater runoff. Harvesting this water is a great way to keep your swimming pool topped up during the months of summer, not to mention for use in other purposes such as irrigating gardens, washing your car, laundry, and toilet flushing.

Water Loss in Swimming Pools

Your swimming pool will lose a certain amount of water per day due to evaporation. Evaporation rates vary depending on your location and the time of the year—evaporation maps are available on Australia’s Bureau of Meteorology website.

It isn’t uncommon to lose 200-300mm during Summer months along Australia’s Eastern coastal regions. If you living in Western Australia, you could lose as much as 400mm in a hot Summer month. This means an average size pool with a surface area of 6m x 3m could lose up to 7,200 litres in one month, approximately 240 litres of water per day.

This is in water evaporation alone, and doesn’t take into consideration backwashing of your water filter, people swimming and splashing about in your pool and the like.

Cost of Filling Swimming Pools

During periods of water restriction, if you need to fill your swimming pool with water, then your local Council will probably disallow you using the mains water supply. Instead, you will be required to buy water from an area outside of the drought affected area. Hiring a truck can cost over $300, and with the water itself it can set you back over $1,000.

To top up your water with mains water supply, many local authorities also require you to meet water efficiency targets, such as using pool covers, installing a rainwater tank, use of water efficient devices and the like. Rainwater tanks are obviously an ideal source of water to use in topping up your swimming pool. Best of all, you don’t need to pay for it, and you can feel good about being self-sufficient and not adding to the drainage of water supplies in dams and rivers in your region.

Automatic Pool Top-up System

Using a rainwater storage tank to top up water in your swimming pool does not have to be complicated. Rain falling on your roof runs to the gutters, where it goes through standard filtration such as water diverters, before the rainwater falls through a strainer into your storage tank. A gauge monitors the water level and an overflow system ensures that excess water is returned to the storm system.

Depending on the type of tank or how far your pool is from the water tank, water can then be gravity fed or pumped into your swimming pool. Your stormwater overflow could even be fed into your pools balancing tank or directly into your pool.

Evidently, you don’t want your swimming pool overflowing with water in a heavy storm, so you should ensure it overflows into stormwater. Optionally, if your swimming pool is close to overflowing, you can always drain water by backwashing it through your filter. The added benefit of backwashing is your filter is kept performing optimally, as all the sediment it has filters gets flushed out.

Optionally, you can install a more sophisticated system. For example, making use of a water leveler device that activates when it detects when water supply level drops in your pool and tops it up with water.

Water Quality for Swimming Pools

Swimming pools will obviously have people swimming in, so you want to ensure the water in your pool is safe. Chlorination of your swimming and chemical balancing will generally disinfect any harmful bacteria or the like that might find its way into your rainwater tank, but there are two things you should consider following in maintaining water quality:

  • Rooftop Material: The material used for your rooftop will decide the suitability of harvesting rainwater from your site. Wood shingles may have been treated with lead or other preservatives, making them unsuitable for health purposes. Other types of materials may absorb water, affecting the amount of run-off you can collect. Location also determines the suitability of a rainwater collection system—severe particulate pollution from heavy industrial areas may contaminate the water.
  • First flush systems, also called rain diverters, are an ideal front line defence for your rainwater tank setup. Many councils require you to install them and they’re not at all difficult to install. These devices flush out the first few litres of rainwater—which often contain dirt, debris, and other pollutants—before it enters the storage tank. Screens also further filter various particles in your rainwater before it enters your tank, as well as keeping mosquitoes and insects from entering your tank.

If you are interested in purchasing a water tank to harvest rainwater for filling up your swimming pool, Clark Tanks offers a range of tanks in varying shapes, sizes and colours. Keep in mind, you can only collect as much rainwater that falls, 1m2 of water hitting your roof yields 1 litre in your tank.


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