Forty percent of New Zealanders rely on groundwater for their drinking supply, but scientists say they don't properly understand the crucial resource and need more funding.
They want groundwater to be more of a priority in the government's freshwater reforms and are holding a conference in Christchurch tomorrow to discuss it.
Groundwater is made up of water in the pores or cracks in sands, gravel and rocks, it comes from rain infiltrating the soil.
People mainly in urban areas such as Christchurch, Wellington and Hawke's Bay rely on groundwater for their drinking supply.
ESR's leading water scientist Murray Close said groundwater was vital to the country's health and economy and provided the flow for the country's rivers.
"Everyone can see the rivers and wants to swim in the rivers, but the fact that actually groundwater is what's impacting those surface waters, you actually need to fix groundwater before you're going to be able to fix the surface waters."
Mr Close said groundwater was little understood and there had been complacency about it because it had been assumed it did not need to be treated in the same way surface water is.
Although he said this had improved since the contamination of the Havelock North water supply in 2016, which affected 5000 people.
Mr Close said there needed to be a coordinated approach to funding specific research on groundwater.
"There is groundwater research at the moment, but what we're saying is it's not adequate to really provide the information we need and to be able to manage our groundwater systems the way they need to be managed," he said.
He said it was urgent because there was a time lag associated with the time groundwater took to flow through a particular catchment.
If something was done now, in some catchments a result could be seen quickly in the next three to five years, in other catchments it could be 30 or for years, he said.
"If we don't do it now, it will be even worse in the future."
Groundwater is not just crucial to the drinking supply, it is also important to agriculture and is abstracted for irrigation.
Scientists say that generally the quality of New Zealand's groundwater is good, but there are variances across the country.
Our Land and Water National Science Challenge director Ken Taylor said there was no question that land intensification has had an affect on the quality of groundwater with nitrates leaching into the supply, but other factors could also cause contaminations.
"We know that other types of land use can have huge impacts and particularly as you get on around say the fringes of cities like Christchurch, where you've got industrial activities that take place over groundwater aquifers. There is a history of industrial solvents and other chemicals finding their way into the groundwater system."
Canterbury's medical officer for health Alistair Humphrey said New Zealand had tens of thousands of waterborne illness cases every year.
"Sometimes there are serious consequences as we saw in Havelock with people dying and other serious complications."
Dr Humphrey said even if people were not as seriously affected often they would lose many days of work, "with thousands of people off work every year from waterborne disease that has a significant cost to the country."
Dr Humphrey said the Ministry of Health needed to be better resourced to properly support drinking water assessors.
The government is undertaking reforms to freshwater and the country's drinking water, wastewater and stormwater systems, respectively known as the Essential Freshwater Programme and the Three Waters Review.
Mr Close said it was critical the government did not forget groundwater as part of these huge reforms.