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Using bathwater to irrigate the garden

Rubber ducky
"What will happen if I water my garden with bath water that has a little soap in it?" --- Heather

Watering a garden with soapy water probably won't be a problem, but it depends on the individual plants being hydrated (and whether you do it once or keep doing it, thus letting problematic compounds build up in the soil).

The main problem from a plant point of view would likely be salt/sodium and/or boron building up. But bleach can also kill soil critters, causing long-term damage to ecosystem health. Bar soap might increase the pH of your water, which would only be a problem if you're watering acid-lovers like blueberries or rhododendrons.

Rainy laundry

The more worrisome problem would be the potential for fecal coliform from bathwater to land on edibles that will be harvested soon (like leaf lettuce), making you sick after you dine. That's why bathwater is often considered more blackwater than greywater (unlike the effluent from your kitchen sink or non-diaper laundry, which tends to be safer). To stay on the safe side, it's better to apply these dicey types of liquid to ornamentals, or to edibles that won't be harvested for several months.

The upshot? Read the label of your cleaning products if you plan to toss them down the drain. Then understand the difference between greywater and blackwater and you'll be all set!

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