The effect of alcohol can be greater in warm weather, say police
Drivers have been warned by Welsh police that they risk losing track of how much they drink at summer parties and barbecues.
As Welsh forces begin their seasonal crackdown, police urged people not to drive at all after drinking.
One in 20 breath tests last summer was positive, and this year's push will involve increased stop checks.
Gwent Police say they will be on the roads 24 hours a day to increase the number of motorists breathalysed.
The campaign, which will be officially launched by Dyfed-Powys Police on 10 June, will also use the Crimestoppers anonymous phone line.
Officers regularly use information on drink-drivers which has been left on the phone line to follow up and catch them.
During the campaign last summer 7,970 breath tests were administered in Wales.
Some 400 of these, or about 5%, were positive.
The four police forces in Wales are joining forces for the campaign.
Dyfed-Powys acting chief constable Andy Edwards said: "In the summer many people take advantage to have parties and barbecues especially when the sun is shining.
"However, as these events may take place over a number of hours they may lose track of how much they have had to drink.
"We would like to remind people there is no set amount of alcohol which can be consumed before legally getting behind the wheel," he said.
"People who drink and drive run the risk of killing themselves, their passengers, and other innocent road users.
"If you are stopped and found to be over the limit you face being disqualified from driving and having a criminal conviction which can have a massive impact on your life.
"The best advice is simple - if you drink, don't drive."
Liane James of South Wales Police said that in warm weather the effect of alcohol on the body could be greater than people might think.
"People caught drink-driving will get a driving ban of at least 12 months and could face up to six months imprisonment and a fine of up to £5,000," she said.