Groundwater levels as far away as Northland plunged after being shaken by the Canterbury earthquake.

Scientists studying the effects of the magnitude 7.1 quake on September 4 are unsure yet exactly how it affected the quality and quantity of Canterbury's groundwater.

But measurements show that in the 24 hours after the big shake and beyond, water levels fluctuated markedly throughout the country.

In Canterbury, groundwater levels fell up to 1.2 metres in some places and rose 6m in others, changes which seem to have been sustained since.

Different water sources in Marlborough dropped nearly half a metre and others rose by 0.8m, while water levelsat the Clyde landslide in Central Otago shot up by 4m.

The height of a groundwater source in Southland fell by 15 millimetres while water at a monitoring site near Whangarei in Northland spiked 39mm higher than before the quake, then dropped to 27mm below the pre-quake level.

Joint investigations by GNS Science, Environment Canterbury, hydrological consultants Aqualinc and Canterbury University reveal almost half of the about 200 monitoring wells in Canterbury have shown long-term changes in levels or trends.

The remaining half of the wells had either short-term fluctuations to the passage of the seismic waves or did not respond at all.

Aqualinc hydrologist Helen Rutter said after short-term changes directly related to quake motion, about one third of Canterbury's monitored boreholes had lower levels of water and the remaining wells had higher levels.

Increased levels were generally across the central Canterbury Plains with decreases in water levels closer to the coast and under Christchurch, Rutter said.

Up to two dozen new springs had broken through across the city, especially from Hoon Hay across the southern city at the base of the Port Hills.

ECan hydrogeology team leader Tim Ezzy said initial work suggested some changes in water quality, with possible cross-contamination between aquifers and other below-ground contamination.

GNS Science geologist Simon Cox said it could take several seasons to fully understand the effects on groundwater and irrigation.

Minute-by-minute monitoring by the Northland Regional Council that showed the impact of the quake on water levels there was "really exciting", he said.

The three researchers are presenting preliminary and provisional results at this week's Hydrological Society Conference in Dunedin.