Not a lake house but I've always shut off my water and hot water heater in my ski house during the week while I'm away.Here is a chart I found on Legionares.It appears that the bacteria will be killed if the tank is brought back up to these temps which is probably why we never hear about this being an issue with water heaters.
* 70 to 80 °C (158 to 176 °F): Disinfection range
* At 66 °C (151 °F): Legionellae die within 2 minutes
* At 60 °C (140 °F): Legionellae die within 32 minutes
* At 55 °C (131 °F): Legionellae die within 5 to 6 hours
* Above 50 °C (122 °F): They can survive but do not multiply
* 35 to 46 °C (95 to 115 °F): Ideal growth range
* 20 to 50 °C (68 to 122 °F): Legionellae growth range
* Below 20 °C (68 °F): Legionellae can survive but are dormant
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SIKSUKR
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