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Ask G: Phosphate debate

Answering the question of whether phosphates are good or bad in laundry detergents.

I'm a bit confused about phosphates in laundry powder and greywater. On one hand, we're told it's better to get phosphate-free products. But I was also told that residue phosphates in greywater help fertilise the garden. What should I get?
- Gloria, NSW

algal bloom in China

Algal blooms like this one in China result from too much phosphate in the water - usually from detergents.

Credit: Wikimedia / Felix Andrews

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Phosphates in detergents soften 'hard water' (water with a high mineral content), allowing the cleaning agents to work more effectively.

Phosphates in fertilisers help plants to thrive, but that's not always a good thing. If phosphate-laden water ends up in waterways, it can encourage algal growth; algal blooms kill other aquatic life and pollute water.

Choose phosphate-free products for the laundry and fertilise your garden with compost made from food scraps and garden waste. If you're using greywater on the garden, you should also consider buying a low-sodium (salt) content detergent.

You can look this up in the Choice laundry detergent tests (