I would not worry. Most nasties ( bacteria and viruses) are quite fragile and they tend not to like sitting in warm water for any length of time. So unless someone was drinking gallons of the stuff there should not be much a hazard. What these needles were doing in a water tank is a really interesting question but I guess we will never know.

Water tanks are a favorite hiding place for syringes; I mean tucked in around the isulation somewhere which is usually nice a warn + dry. I'd guess these just got dropped into the water itself accidentaly. Plumbers etc should be aware of this and approach with caution.

JWK ascertains that 60C is the temperature required for maintaining hot water systems - then through a leap of imagination s/he links the elimination of waterborne pathogens with assumptions on the elimination of bloodborne virus. A Kurdziel would not worry since his/her understanding is that 'most nasties (bacteria and viruses) are quite fragile and they tend not to like sitting in warm water for any length of time', and goes on to anticipate ingestion as the route for infection. How bizarre this all is and indicative of the need for caution, and perhaps also the need for counsel. In fact, the risk is firstly from sharps injury and in this regard there is remarkably little information about the heat resistance of bloodborne virus agents. After all, it is not the main focus of the public health problems that they cause. The second problem that has not been mentioned is that you have one person, maybe three - or maybe even more if they are sharing needles - working on your site while high on illicit drugs. What are they doing and how will their actions affect your business, your other employees, and members of the public?

Are the loos lit? If so, blue filters on the lights generally discourages IDUs since it becomes difficult to find a vein