"There are two reasons people drown, predominantly, they don't have the skills to get themselves out of trouble but in most cases people make bad decisions."
A preventable death was one where water safety intervention could have had an influence and helped prevent the incident.
Only nine people aged over 65 drowned in preventable deaths in 2016 but the number had been increasing since, to 14 in 2017 and 17 last year.
Twelve had died already in New Zealand throughout 2019 with slightly under a fortnight left in the year.
However, the 2016 year was an anomaly after 10 people died in preventable drowning incidents in 2014 and 12 a year later in 2015.
And since 2014, the only age bracket which had recorded more preventable deaths were those aged 15 to 24-years-old with 88.
Mills, who believed one preventable drowning was one too many, couldn't pinpoint where the issue arose for elderly people but said those who died were often alone.
"People are living longer, healthier lives, they're retiring and might have a bit of money in the pocket and they're jumping into the water in their droves," he said.
"Maybe they're not as fit as they used to be … of the drowning in that bracket, two thirds of them are alone when they do get into trouble."
Earlier this month, Water Safety NZ rolled out new technology which the organisation hoped would help prevent "dumb drowning".
An artificial intelligence bot had more than 40 years of water safety data banked into its system to help it predict when the next drowning would take place.
The bot also used weather forecasts, tides, and where people could buy alcohol near the water to predict the "drowniest" days.
Mills hoped the data and insights provided by the bot would allow WSNZ to more accurately target water safety messages to Kiwis.
Preventable drowning incidents were worst across Northland, Auckland, Bay of Plenty and Waikato, with an eagle-eye to be kept on these regions.
The numbers of people aged 65-years or older who died in preventable drowning incidents also reflected this, with three dying in the Waikato region over 2019.
Northland followed with two and Auckland, Canterbury, Hawke's Bay, Otago, Southland, Wellington and West Coast with one.
People in and around the water throughout summer should know their limits before getting in, Mills said.
"We're not the fun police and want everyone to enjoy the water in every way, shape or form, it's part of our culture, our DNA," he said.
"We want people to [have fun] - we just want them to come home safely.
"For us it's about knowing your own limits, having knowledge and awareness and making good decisions around the water. Stop and think about it - if in doubt, don't go in."
Other alarming elderly preventable death statistics
• Eight NZ Europeans aged 65-plus had drowned preventable deaths, two ethnicities were unknown, one was a Pacific Peoples and another was classed "other".
• Tidal waters and rivers were where most of the elderly drowning deaths took place, with three-a-piece.
• Most of the elderly deaths involved a powered boat, with five deaths. Accidental immersion events were second with three.
Top tips to stay safe around the water this summer
1. Choose a life-guarded beach and swim between the flags
2. Read and understand the safety signs - ask a lifeguard for advice as conditions can change regularly.
3. Don't overestimate your or your children's ability to cope in the conditions.
4. Always keep a very close eye on young children in or near the water - keep them within arm's reach at all times.
5. Get a friend to swim with you. Never swim or surf alone.
6. Watch out for rip currents, they can carry you away from shore. If caught in a rip current, lie on your back and float, put your hand up and call for help.
7. Be smart around rocks: When fishing, never turn your back towards the sea and always wear a lifejacket.