- ✓Brisbane tap water is safe throughout taste events. MIB and Geosmin are non-toxic taste compounds. Seqwater monitors continuously and publishes water quality data throughout.
- →The earthy taste comes from MIB and Geosmin — compounds produced by Actinobacteria and cyanobacteria in Wivenhoe Dam during warm water periods. Detectable at 5–10 nanograms per litre — far below any health threshold.
- →Two taste windows per year: January–March (summer algal growth) and May–July (seasonal reservoir turnover). Moreton and Gold Coast zones (North Pine Dam supply) are typically less affected.
- ✓Quick fix: leave tap water uncovered in a jug in the fridge overnight — MIB and Geosmin are volatile and off-gas significantly. Improvement is noticeable.
- ✓Permanent fix: under-sink RO eliminates the taste entirely. High-capacity catalytic carbon also significantly reduces both compounds.
What happened in summer 2025–26
Brisbane tap water has an earthy, musty or "dirt" taste that returns predictably each summer and again around May–July. The 2025–26 summer event began in December 2025 and continued through January and February 2026, with Seqwater's Wivenhoe Dam recording elevated concentrations of MIB (methylisoborneol) and Geosmin — the two compounds responsible for the distinctive taste.
Seqwater confirmed throughout the event that water met all health standards. The taste compounds are non-toxic. They are produced by naturally occurring Actinobacteria and cyanobacteria that thrive in warm reservoir water, and they are detectable by the human nose and taste at concentrations as low as 5–10 nanograms per litre — far below any health threshold.
Why Brisbane water tastes this way — the seasonal pattern
Wivenhoe and Somerset Dams, which supply inner Brisbane via the Mt Crosby Water Treatment Plant, experience two predictable taste windows each year: January–March (summer algal growth as water temperatures peak) and May–July (as seasonal turnover mixes deeper water containing decomposing organic matter to the surface).
Seqwater uses Powdered Activated Carbon (PAC) dosing during these events — injecting fine carbon powder into the raw water before treatment to adsorb MIB and Geosmin before they reach the distribution network. PAC dosing reduces but does not eliminate these compounds during severe events, because at very low nanogram-per-litre concentrations the human palate is extremely sensitive to both.
Water from North Pine Dam (supplying Moreton, Redland, Logan and Gold Coast zones from the north-west) does not typically experience the same severity of taste events — residents in these zones are usually less affected.
What actually removes the earthy taste
The effectiveness of different approaches for MIB and Geosmin removal, in order:
- Reverse osmosis (best): RO membrane completely removes MIB and Geosmin as part of its comprehensive dissolved contaminant rejection. If you already have an under-sink or countertop RO, your water will taste clean regardless of reservoir conditions.
- High-contact-time activated carbon (good): Carbon adsorption is the mechanism Seqwater itself uses (PAC dosing). A whole-home catalytic carbon system with good contact time significantly reduces MIB and Geosmin. Under-sink carbon is more effective than pitcher filters due to higher-density media and better contact time.
- Pitcher filters (limited): Some improvement during mild events. GAC pitcher filters have limited contact time and may not fully address severe taste events. Activated carbon pitchers with dense carbon block media perform better.
- Letting water stand open (overnight): MIB and Geosmin are volatile compounds that partially off-gas. A jug of water left uncovered in the fridge overnight will taste noticeably better than water poured directly from the tap. Not a complete solution but an easy immediate step.
Never stop drinking tap water because of earthy taste during these events. Seqwater monitors continuously and the water is safe throughout. The taste is cosmetic — not an indicator of contamination.
Is it getting worse?
Anecdotally and from Seqwater's published data, taste events have become more frequent and intense over the past decade, correlating with warmer average water temperatures in Wivenhoe Dam. This pattern is consistent with the broader trend of increasing water temperatures in southeast Queensland reservoirs.
For households who find the seasonal taste events a genuine quality-of-life issue, an under-sink RO or high-capacity carbon system is the permanent solution. The investment is justified not just for taste events but for Brisbane's year-round water profile — chloramine city-wide and 115 mg/L hardness in inner zones.
Brisbane summer taste events are predictable, manageable and well-understood. Seqwater's response (PAC dosing) reduces but does not eliminate the compounds during severe events.
For households who want consistent taste year-round: under-sink RO is the permanent fix. A high-capacity catalytic carbon system is the next best option. In the meantime: fill a jug from the tap and leave it uncovered in the fridge overnight — the compounds are volatile and significant off-gassing occurs within a few hours.