As Vancouver increasingly relies on an underground aquifer to water its street trees and the Langara golf course in the midst of this summer’s punishing drought, one hydrology expert is cautioning that we don’t know enough about how readily it can be replenished.

For more than 25 years, Vancouver’s parks department has used the city’s largest aquifer to irrigate its Langara golf course, taking pressure off the region’s treated drinking water supplies.

Now, as the Lower Mainland experiences a drought that shows no signs of ending, Vancouver is considering gently expanding its use of the vast underground Oakridge aquifer for non-potable water needs. It comes as the city goes to extremes to save water, including salvaging it out of a soon-to-be replaced watermain in order to flush back lanes in the Downtown Eastside for health and safety reasons.

As homeowners face an outright ban on lawn sprinkling and car washing, and some industries slow or halt production to save water, the city is using two abundant wells it drilled in the 1990s to keep crucial trees alive and to water greens and tee-off boxes at Langara. It is also considering refurbishing a silted well at the McCleery Golf Course to get those greens off the city’s main water supply. It says it barely draws down the vast capacity of the aquifer and monitors levels regularly.

But a water expert with Simon Fraser University cautions that tapping into groundwater aquifers to get around water restrictions is not a good idea in the long term.

“The issue with Vancouver is we have not really mapped our groundwater sources. We don’t have adequate knowledge of our aquifers,” said Steve Conrad, a water energy instructor at Simon Fraser University’s School of Resource and Environmental Management.

“I generally don’t think groundwater is a good option for managing drought.”

Conrad said aquifers are large underground bodies of water trapped in the ground and are recharged by surface water run-off. In some cases, the aquifer is contained in a basin. But others are essentially underground streams. Those, he said, are more at risk of depletion if they are too heavily used, particularly in dry conditions.

City engineers and the park board say they have a lot of data about the Oakridge aquifer and they believe it is capable of supplying up to 120 US gallons per minute, or about 7.5 litres of water per second, year-round.

The aquifer, which runs under the western half of the city, is part of a larger underground aquifer called the Quadra Sands, which stretches from Point Grey through to Burnaby and New Westminster. It is bordered on the south by half a dozen aquifers linked to Fraser River sediments.

The city is nowhere close to reaching Oakridge’s maximum capacity, and instead is only lightly using the aquifer to irrigate Langara golf course, according to Brian Crowe, Vancouver’s director of water, sewers and district energy. Oakridge Mall has tapped into the aquifer since the 1970s to use water as a coolant. The city has also designated it as an emergency drinking water supply in the event of a major disaster such as an earthquake.