2009/14 + 2019/20 – Yarrawonga (Victoria) – Turbidity, Taste & Odour

Yarrawaonga – Victoria – Turbidity

2009/10: Yarrawonga Turbidity 6.3NTU

2012/13: Yarrawonga Turbidity 10NTU

2013/14: Yarrawonga Turbidity 5.7NTU

Chlorine-resistant pathogen reduction: Where filtration alone is used as the water treatment
process to address identified risks from Cryptosporidium and Giardia, it is essential
that filtration is optimised and consequently the target for the turbidity of water leaving
individual filters should be less than 0.2 NTU, and should not exceed 0.5 NTU at any time
Disinfection: A turbidity of less than 1 NTU is desirable at the time of disinfection with
chlorine unless a higher value can be validated in a specific context.

Aesthetic: Based on aesthetic considerations, the turbidity should not exceed 5 NTU at the
consumer’s tap.

2020: Yarrawonga (Victoria) – Taste & Odour

Murray River Taste and Odour Event

Some towns in North East Water’s region supplied from the Murray system were affected by a taste and odour event from Australia Day in January through to March 2020. The taste and odour event was caused by naturally occurring taste and odour compound known as geosmin. This organic compound has a very strong, earthy taste and odour that is unpleasant. The compound can be produced by blue-green algae, bacteria and sometimes protozoa, and can be smelled at very low concentrations (around 10 ng/L). The compounds are generally present in drinking water but below noticeable levels. Geosmin can cause objectionable taste and odour in drinking water, but is an aesthetic issue only, with the water remaining safe to drink. In late January 2020, an algae bloom occurred in Lake Hume that produced extremely high concentrations of geosmin. The dominant algae species was Dolichospermum c.f. crassum, a known geosmin producer. This bloom subsequently spread downstream to Wodonga, Wahgunyah and Yarrawonga offtakes. This taste and odour event eventually spread much further down the Murray River and affected water utilities on both sides of the Victorian and NSW border.

Traditional treatment processes do not fully remove geosmin and instead powdered activated carbon (PAC) is dosed to adsorb the compound before removal via filtration. All of North East Water’s Murray system towns have this process in place, however, the concentrations of geosmin in the source water were so high that regular dose rates were unable to fully remove the compound from the treated drinking water. North East Water’s Yarrawonga supply experienced the highest concentrations of geosmin, peaking at 1,800 ng/L (see Table 3-27 for full results). This is the highest concentration ever recorded by North East Water. This resulted in a high rate of customer complaints relating to the taste and odour of water in localities supplied by Wodonga, Wahgunyah and Yarrawonga systems. The Corporation implemented customer communication via social media while the Operations teams were busy upgrading PAC dosing systems to achieve higher dose rates. North East Water 2019/20 Drinking Water Quality Report