The most painful part of his weight loss journey wasn't cutting back on the booze, or refraining from snacks - it was replenishing his wardrobe.
"I saw it as a bloody cost, it was a lot of money," he said, "But I had suit jackets hanging up in the closet that looked like circus tents."
Mr Dalton's wallet shrunk along with his waistline as he shelled out thousands on clothes to fit his new 97kg frame, but his new suit jackets reflect his progress, being two sizes smaller than those he used to wear and "could never even button up".
Six months ago, it was the mayor's youngest son whose beneficial weight loss made Mr Dalton realise he needed to do something, though he marks all three of his children as "the major incentive".
His weight hadn't worried him from an aesthetic point of view, but he wanted to shed some kilos to improve his health - this seems to have worked, as his weight loss has allowed him to sleep without a CPIC machine after suffering sleep apnea for the past 12 years.
Napier City Council chief executive Wayne Jack had also noticed an increased amount of energy from the mayor, and described his weight loss as "transformative".
Mr Dalton admitted he had always been overweight, but "the social aspect of being mayor of the city" caused him to pile on more until he reached 120kg.
"You're always being invited to lunches and cocktail parties and things like that," he said.
"I could be at social functions every night, where the first thing they do is hand you a glass of something, and there are trays of food constantly floating past."
But when he decided to shed the extra weight, he also decided this goal wouldn't interfere with his job.
"I don't think it actually matters how you do it," he said, "but if you try to do something that interferes too much with your social life, or with your work life, you're on a path to failure."
Whether this involved pretending to drink at social functions, or eating dinner earlier, it was all about fitting his diet in with his job rather than trying to adjust his lifestyle to fit a certain diet.
If he had a breakfast meeting with an extravagant spread, he wouldn't eat again until his evening meal.
Likewise, if he had a dinner event he would miss lunch or breakfast.
"Like everybody that's overweight, I've had a go at most diets, and frankly they require a helluva lot of discipline," he said.
"That's difficult with the lifestyles we lead these days."
He took parts from different diets until he found a method that worked for him, even trying fasting, though never sticking to it religiously.
"At the end of the day if you have the propensity to be overweight, then you've got to change your lifestyle," he said.
"You've got to adjust things, you've got to fit a healthier regime inside your everyday, but don't try to change your everyday because that's what you are."
Fitting exercise into his already busy schedule wasn't an easy task, as his job required a lot of sitting down and talking to people; which he realised wasn't using a lot of energy.
"I incorporate exercise into my day, rather than specifically going out and exercising," he said, which can sometimes involve strategically planning his parking in order to walk more.
Mr Dalton is not the only one at the council who has shed a few kilos, with a number of staff focusing on getting fitter and eating healthier through the council's Wellness Initiative.
Now in its third 12-week programme, the council has been visited by dieticians, personal trainers, and nurses, and runs lunchtime yoga classes twice weekly.
"There's been a massive difference to staff wellbeing," Mr Jack said.
"We've reduced sick days and increased productivity, especially in the afternoons."
Mr Jack introduced the initiative as he believed employee health and wellbeing boosts organisation health, and the success of the programme is clearly shown by the fact that the majority of participants say they felt fitter.
Corporate communications manager Robyn Mclean said the mayor's weight loss was great for staff to see and proved that anyone can do it.
"It's great to have Bill, who is the front person of the council setting this great example" she said, "it's amazing."
For now, Mr Dalton is happy with his new weight.
"I think the insurance charts say I should be 78 kg or something, but I haven't been 78 kg since I was about 12 years of age" he said.
"I'm comfortable, I feel good, and I have lots of energy."
Bill's tips for losing weight
•At social events, sip from a wine glass filled with water.
•Avoid rigidity. "If I want to eat a piece of chocolate, I'll eat a piece of chocolate ... if you say 'I'm going to give up drinking' and you're a drinker, well you're setting yourself on a path to failure."
•Donate old "120kg"clothes to op shops, or the Napier Operatic Society (but keep some "108kg" clothes in storage, just in case).
•Forget about it occasionally - events and holidays are times to "eat, drink, and be merry" but then "incorporate weight loss into [your] working day for a while".
•Let your lifestyle dictate your diet, don't let your diet dictate your lifestyle.
