What size cold water tank do I need?

[tireetim]

I've got a vented hot water cylinder (160L) that heats water with an immersion. It's the only hot water for the house and will be used for 4 sinks (15mm pipes) and a bath (22mm pipe). Can anyone advise me what size cold water tank I need for this in the loft? Nothing else will come from the cold water tank (all showers are just electric with a mains water feed and the bath cold tap will just fill from the mains). My options seem to be a 25 Gallon or 42 Gallon.
Thanks.

 

[Burnerman]

Tanks are available up to 100 gall capacity, and can be added to in parallel if necessary.
Your typical 42 gallon one should be fine and they often come with a byelaw 30 fitting kit too.
Often the size of the loft hatch makes the choice for you!
Use a part 2 ball valve.
John