we need to purchase an electric water heater. It will be used to supply hot water to a kitchen in a senior center. There is a high pressure dishwasher and three sinks. I need to know if a 50 gal. residential tank will suffice or do we have to go to a commercial wh. There will only be 3 - 4 hours daily that the kitchen will be in use.

I'm not sure how the health department is where you are from but here commercial dishwashers must wash at 180f unless chemicals are used in the washing. A standard 50 gallon electric will never keep up the temp at 180 best call the health department first before making any purchase

Plumber Palmer gives you excellent advice; do what he says. You will be needing at least an 80 Gallon Commercial Water Heater to meet requirements of the Health Department I venture to guess. But contact them to reduce liablity.

also, they do make a small booster water heater that will give you the necessary temperature for the dishwasher.