There is no requirement for regular pool inspections. Those councils which were able to carry out inspections found around half of pools failed safety standards.
Once the bill takes effect on January 1, all swimming pools will have to be inspected and certified by the council or a professional organisation every three years.
Councils will be able to issue warning notices rather than prosecuting non-compliant owners, Smith said.
The bill also scrapped rules which Smith said were "unworkable", in particular the mandatory fencing of spa pools or hot tubs, of which there are around 100,000 in New Zealand.
Instead of fencing, those pools will now require a lockable cover.
"I know there are members who have opposed the practical changes in the bill around these spa pools," Smith said.
"I would simply point out that ... more children have been drowned in baths than in spa pools, and no one in this Parliament is seriously suggesting that we should have to put a fence around a bath."
Infinity pools or pools next to cliff of 20 metres or more will no longer need a fence on all four sides.
Labour MP David Parker said his party would have backed the bill if National had removed a change which allowed alarmed gates to be used instead of automatically locked gates.
National had "stubbornly and wrongly refused" to agree to its sole concern with the legislation, he said.
"We wanted locked gates or doors around pools because we did not think that alarms were an adequate protection for children."
Parker said alarms were too easily ignored, and many alarm systems were likely to stop working within the three-year inspection period.
The Green Party also opposed the legislation.
Green MP Eugenie Sage said that under the current rules, which came into force 30 years ago, the number of drownings by children under five years old had fallen from 10 to three.
"If it is not broken, why deal with it?" she said.
She noted that paediatricians, Starship Hospital, Plunket and Water Safety New Zealand had all spoken in support of the existing rules.
Sage expressed concern about provisions which allow pool owners to be granted waivers if there are no significant risks to children.
The bill also replaced the term "fence" with "physical barrier", which created more uncertainty and flexibility for councils, Sage said.
CHANGES
• Three-yearly pool inspections by councils
• Spas and hot tubs need locked covers, rather than fences
• Garden pools and drainage ponds don't need fences
• Alarmed gates which do not automatically locked are allowed
• Infinity pools and pools by a 20-metre cliff do not need four-sided fencing
