Costs of upgrading Alexandra's domestic water supply were discussed at a Central Otago District Council meeting yesterday.
Six years of investigations have resulted in two upgrade options, with estimated initial costs of $8.5 million or between $11.5 million and $14.5 million, and respective estimated increases of $550 to $650-$800 on annual rates.
For the past 35 years, water has been sourced from six bore sites on the true left bank of the Clutha River, near Eclipse St.
In addition to hardness and scaling issues and proximity to old mine workings and a former landfill, the water supply does not meet new drinking water standards set by the Ministry of Health.
Under those standards, Alexandra water has an E grading, the worst possible, and there are also occasional taste and odour issues with the supply.
The options presented yesterday were a supply based on water from the Clutha near the present supply source, or from near the Clyde bore, which also does not meet drinking water standards, on the shores of Lake Dunstan.
Council development engineer Peter Morton said all other options had been exhausted, as he presented two to councillors.
He said they were the most ''realistic'' of the 10 identified in a report from hired consultants.
The most affordable of the two was to use the existing bores with ''direct filtration'' and appropriate disinfection. That would not, however, address the lime scaling issue, which was the cause of most complaints by users.
The capital works for this option had a price tag of $8.5 million. Over a 20-year period, operating and maintenance costs would bring that up to $14.5 million.
The option favoured by council staff would cost an estimated $11.5 million to $14.5 million.
Over 20 years, that would increase to $16 million to $21.2 million.
Under this option, water would be sourced from Lake Dunstan or the Clutha River, only Alexandra would be serviced, and scaling would be significantly reduced.
Investigations during the past six years have considered options to service Clyde and the Dunstan Flats from the upgraded Alexandra supply. While that might provide cost benefits, it could also delay the upgrade.
For that reason, Mr Morton recommended the council focus on Alexandra.
He said of the two sites, Lake Dunstan ''appears to be the most economical but [is] not yet proven''.
The council's long-term plan has $500,000 set aside for the upgrade in this financial year, $4 million next year and $3.1 million in the following year.
From this year's funds, an estimated $110,000 will be used to install trial bores to investigate the feasibility of supplying Alexandra from the Lake Dunstan shoreline gravels near the Clyde water intake.
