How do you prevent root rot in houseplants growing in water?

To prevent root rot in houseplants growing in water, ensure that the container allows for good drainage and avoid over-filling it. Change the water regularly, ideally every week, to prevent stagnation and the buildup of harmful bacteria. Additionally, use clean, fresh water and consider adding a small amount of hydrogen peroxide to help oxygenate the water and inhibit rot. Finally, monitor the roots for any signs of decay and trim away any affected areas promptly.