Mayfair Pools and Spas owner Mike Freeth says draining your swimming pool could create a "big dangerous hole" in your back garden.

The pool fence versus pool cover debate could soon become even more draining for some pool owners.

The Marlborough District Council has sent letters out to people with expired pool covers urging them to take "immediate" action as pool covers were no longer "an acceptable [safety] solution".

Recommended solutions included putting up a temporary barrier, or draining pools to 400 millimetres or less.

The move comes after the Ministry of Business, Innovation and Employment ruled that automatic pool covers, as a barrier, did not comply with the Building Code.

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Pool owners with expired waivers, previously allowing them to have a cover, would be given 90 days to install a permanent fence around their pool after they received a 'notice to fix' from the council.

JACKSON THOMAS/STUFF The ministry has warned draining your pool could create a drop of more than a metre, also forbidden in the Building Code.

Although, they would need to get building consent before putting up a new fence, a council spokesman said.

The council had "no choice" but to enforce the regulations handed down by the Ministry of Business, Innovation and Employment, he said.

"The property owner is required to take whatever immediate steps are required to ensure that the pool area is inaccessible to a child under 6 until the compliant barrier is consented and installed," he said.

RICKY WILSON/STUFF Swimming pool owner Warren Cairns, of Blenheim, said electric pool covers might actually be safer than fences.

"In the interim, owners can make their swimming pool safe by putting up a compliant temporary barrier or lowering the water level of the pool to below 400 millimetres.

"Council will work individually with each owner to get their building consent and start planning their fence installation. Winter is an ideal time to do this, when pools are not being used."

Close to 40 pool owners had been told to take action, but there were another 200 people in the region with pool cover waivers that would soon expire.

Mayfair Pools and Spas Marlborough owner Mike Freeth believed draining the pool until a fence was built would make it "even more" dangerous.

Freeth said draining the water to 400mm would create a "big dangerous hole" in people's yards.

"The thing is, most swimming pools have a deep end and most deep ends would be 1.5-metres or more.

"So if you're going to drain the swimming pool down to 400mm, or empty it right out, someone falling into that empty swimming pool, is going to do damage to [themselves]," Freeth said.

The depth of 400mm was in place to allow for water features such as fish ponds, he said.

"A 2-year-old crawling across the concrete and falling into an empty swimming pool is going to do more damage than falling into water.

"At least with water someone has a chance of diving in and getting them back out, but if they fall off a patio into an empty swimming pool, the survival rate is probably not going to be too high," Freeth said.

Falling onto a pool cover was much safer, he said.

"If you step backwards and step into a filled up pool with an auto pool cover it would be like jumping on a water bed."

Ministry performance and engineering manager building Dave Robson said the Building Code did not allow any drops of more than 1m, which pool owners would have to consider if draining a pool.

People would need to discuss what determined a "compliant" temporary barrier with their council, Robson said.

The ministry would continue to update and review the Building Code to "ensure best practice", Robson said.