In most provinces, hot tub water is classified as grey water, which means that the regulations for safe disposal are governed by either provincial building codes or health regulations. So, check with your local building authority or public health unit before you dump your water.
It’s never safe to drain straight into the lake, and in some provinces, it’s illegal to discharge grey water directly onto your property—it must be disposed of through a sewage system. But loading up your septic tank with 1,700 litres of water at once is going to flush out the bacteria that keep the system functioning.
Instead, one week before you intend to drain the tub, stop adding chemicals and leave the cover off. Chlorine and bromine, the most common sanitizers in tub water, evaporate when they’re exposed to air. You can help expedite this process by turning off the heater and running the jets for a few hours.
Once the chlorine or bromine levels are close to zero, you can start pumping out the water into your septic system in small batches over a few days.
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Hot tub: do's and don'ts