Hong Kong’s tap water comes primarily from Dongjiang (East River) in Guangdong province, supplemented by local reservoirs. The Water Supplies Department maintains it to World Health Organization standards, making it perfectly safe to drink — but “safe for humans” and “ideal for plants” are two different things.
What’s in Hong Kong tap water?
Like most municipal water supplies, Hong Kong’s tap water is chlorinated and fluoridated, and it tends to be moderately hard, meaning it contains dissolved minerals like calcium and magnesium. The pH typically hovers around 7 to 8, making it slightly alkaline. These characteristics matter quite a bit when you’re watering plants regularly.
For indoor plants
The chlorine and chloramine used in treatment can mildly stress sensitive plants over time, particularly ferns, peace lilies, and spider plants. The fix is simple — leave a jug or watering can of tap water uncovered overnight. Chlorine dissipates readily into the air, though chloramine (if used) is more stubborn. For very sensitive tropicals or orchids, this resting period makes a noticeable difference.
The slight alkalinity can also be an issue for acid-loving plants like gardenias, azaleas, and most ferns, which prefer a lower pH around 5.5 to 6.5. Over many months of watering with alkaline tap water, the soil pH can creep up and cause nutrient deficiencies — yellowing leaves being the most common symptom. Adding a tiny squeeze of lemon juice or a splash of diluted white vinegar to your watering can occasionally can counteract this.
The mineral content is generally not high enough to cause serious problems for most common houseplants, though you may notice some white crusty residue building up on terracotta pots or soil surfaces over time. This is just mineral salt accumulation and can be managed by periodically flushing the soil thoroughly.
For cut flower bouquets
For vase water, Hong Kong tap water is absolutely fine for most cut flowers. Roses, lilies, chrysanthemums, and similar common bouquet flowers are quite tolerant. However, a few things help them last longer. Using room-temperature water rather than cold straight from the tap reduces the shock to the stems. Adding the flower food sachet that often comes with bouquets is worthwhile — it contains a mild acidifier, sugar for nutrition, and a biocide to slow bacterial growth, all of which counteract some of tap water’s less-than-ideal qualities.
Changing the vase water every two days and re-cutting the stems at an angle makes a bigger difference than water source for longevity. That said, if you want to go the extra mile for particularly delicate flowers like sweet peas or garden roses, filtered or rainwater can give them a slight edge.
Bottom line
Hong Kong tap water won’t harm your plants or flowers, but it isn’t perfectly optimised for them either. Letting it sit before watering, occasionally adjusting the pH for acid-lovers, and not overthinking it for cut flowers will get you 95% of the way there. Rainwater, if you can collect it from a clean source, remains the gold standard for houseplants — but given Hong Kong’s sometimes-polluted air, tap water that’s been left to rest overnight is often the more practical and reliable choice.