With the latest purchase, almost all of Featherston's waste water will eventually be irrigated on to the land, instead of into Donald's Creek, which ends up flowing into Lake Wairarapa.
South Wairarapa mayor Adrienne Staples said originally the council planned to install a high rate treatment plant as there was no suitable land in Featherston but a piece of land came on to the market.
"We purchased the land earlier than anticipated because it presented an excellent opportunity when it came on the market.
"This is a wonderful opportunity for SWDC to become one of the few local authorities in the country to have a fully environmentally friendly system which discharges almost 100 per cent of its output to land."
The acting chief executive of the council, Mark Allingham, said it was cheaper in the long term than a new plant and also a more culturally acceptable solution.
"Also, a plant needs to be renewed over time where land can be used forever and produce hay rather than waste."
Currently the waste water, which includes sewage from toilets, trade wastes and water from washing machines, showers and baths, is treated in an oxidation pond system from the 1970s, with ultraviolet disinfection and then discharged into the creek.
It contains nitrogen, phosphorous and ammonia which negatively affects waterways and aquatic life but act as nutrients on land.
Mrs Staples said the plan was consistent with the Government's National Policy Statement on Freshwater, the proposed regional Natural Resources Plan and the SWDC's wastewater policy which was adopted in 2011.
Resource consent for the high rate treatment plant, due to be heard in November 2015 by Greater Wellington Regional Council, would have to be amended.
Mrs Staples said the project had to be spread over a long term to keep rates affordable.
"We have to balance the environmental impact against affordability.
"It will still take some time to be able to afford the irrigation infrastructure and we are looking at how to minimise the impact on rates."
The council is assessing whether existing irrigation infrastructure on the purchased land could be used in future.
Mrs Staples said the cost of the purchase was being kept confidential at this stage, at the request of the vendor, until the sale process was completed.
Mr Allingham said there were a number of plans, as part of the consent, to monitor the disposal method.
Plans involved only discharging enough wastewater to be taken up in the soil to avoid any filtering into ground water, odour control, and wind speed restrictions meaning irrigation must stop if maximum speeds were reached.
Featherston's leaky pipes are also expected to be fixed under the plan.
