"Detecting Covid-19 in wastewater samples can help alert local communities to be more vigilant, keep up hygiene measures, and get tested and stay home if they are unwell."
The ministry said areas where testing was conducted was determined through a mix of variables, including population size and proximity to managed isolation facilities.
It did not respond to the Chronicle's questions around when wastewater testing began in other towns such as Taupō and Gisborne, which have similarly sized populations to Whanganui and are also not home to MIQ facilities.
Both Whanganui DHB chief executive Russell Simpson and Whanganui MP Steph Lewis said they weren't concerned wastewater testing only began in Whanganui last week.
"The fact we've got the capability to do it now is excellent, a lot of other places haven't," Simpson said.
"In fact, a place the size of Whanganui having the ability to test the wastewater is a positive thing.
"I think it's a real evolving issue. It's not just as simple as taking water and testing it - there's a whole complex process that goes into testing it.
"I'm really encouraged that it is available now."
Lewis said there was likely a reason Whanganui hadn't had wastewater testing earlier.
"I think the Ministry of Health is well aware of Whanganui because they put out the stats each week around things such as vaccination rates.
"Places like Gisborne and Tauranga, we have port workers and people on ships in those areas. It's an additional tool like surveillance testing."
According to the Ministry of Health, the first wastewater testing results from Whanganui should be available this week.
