A quarter of private swimming pools checked by the Auckland Council this year were found to be unsafe.
The council made more than 13,000 inspections of the region's 31,000 registered pools in 2023.
Pool compliance leader Stuart Airs said faulty gates were the most common reason for a failed inspection.
He said access to pools through faulty gates was one of the leading causes of drowning in preschoolers.
"While the council conducts safety checks of all registered pools every three years, pool owners need to stay vigilant and make sure pool access points are secure."
Another common risk was portable pools left full of water and without appropriate barriers.
"Portable pools are a popular family Christmas gift, and some on the market now are almost as large as traditional in-ground pools. Unfortunately, many people set them up without the proper barriers in place, and we have seen tragedies occurring at this time of year as a result."
Any pool with water deeper than 40cm needs a barrier or fence by law, he said - even paddling pools. Above-ground pools did not need a fence if they were at least 1.2m high, but access had to be restricted to avoid accidents.
"Nobody wants to lose a loved one to a home drowning accident," Airs said.
"By being proactive with regular maintenance checks of gates and latches, ensuring young children cannot access pools on their own and always keeping eyes on children around water, you can help to keep your whānau from ever being in this position."
The council has an inspection checklist online.