legionella

You can get nasties like legionella growing in tanks if the temperature is hot but not hot enough to kill them.

Just a note, you should heat the water up every now and then to kill any legionella bacteria.

To kill legionella you need to water at 140 F (60 C) or over, for more than 30 minutes.

If they're not kept hot enough they could be breeding ground for Legionella and a whole raft of other bacteria.

Going less than 55 °C tap temperature / 60 °C in the tank is bad though, at least in larger installations - otherwise, you risk legionella and other microbial infestations [1].

Typical temperatures for heat pump derived DHW are around 120F (45-50C), with some (bi)weekly cycles to avoid legionella build up at 150F(65C).

If you only have 50C in your tank and badly insulated lines, your temperature can dip below 50V very easily where legionella feel really comfortable.

Do legionella multiply faster in a heat exchanger than a river?

It's not safe to drink dehumidifier water due to Legionella risk.

If you set your boiler to 45°C in a country with (nearly) unchlorinated water you'll have a nice Legionella culture after your 3 week vacation.

Depending on how you plan on using that water, you also have to make sure the temperature never dips below ~60C to avoid legionella from spreading.

I had no idea that legionella risk was a thing for data centers.

Yes, I saw DIY heat exchangers posted in the past and people were worried about Legionella/Legionnaires and mold.

That is minimum temperature of the heated tap water(Legionella and other diseases).

You should be more worried about Legionella, but proper steam and hot water systems will stay above 140F (60C) as that temperature not only prevents the bacteria from multiplying but will kill 90% of them within 2 minutes.