North Wales Police is issuing SmartWater spray to high-risk victims to further protect them against domestic abuse.
The forensic liquid is often used to mark property to prevent items being stolen.
But the force is now giving out DeterTech canisters to some victims to prevent perpetrators from contacting them.
The substance in each canister, only visible under ultraviolet light, has its own unique reference number, similar to a DNA profile.
Once it is sprayed, the watermarks will provide key evidence in court against a suspect, who is likely to have been ordered not to visit a victim.
Inspector Claire McGrady said: “The spray leaves watermarks on skin and clothing, which isn’t easily washed off.
“Clothing can go through a wash cycle a number of times and a person can have multiple showers and traces of the substance will still be visible using a UV torch.
“Once the spray has been identified, samples are taken and sent to forensics so we can match the product to a person.
“That evidence can then be used in court to prove a perpetrator has been in the presence of a victim.”
Suspects will be told victims are protected by the forensic spray and will be given a notice to explain how it works.
The spray can also be used to mark items to prevent them from being stolen.
Inspector McGrady added: “Domestic abuse cases can often be difficult to prosecute. Victims can find it difficult to pursue cases because of lack of evidence, and because the process to get to the prosecution stage can be lengthy and traumatic.
“We’re hoping in some cases, this new SmartWater spray will provide better evidence and make the process a lot easier for victims.”
