Water on downstairs no water upstairs.

Hi Everyone.
I have a 3 story house and want to split into a separate flat for each level.
When the tap is on downstairs there is no water upstairs and it all drains back down the pipe. got good pressure upstairs when nothing else is on. I have a 25mm alcathene pipe coming in to the house.
Just wondering what to do? put 2 t's on the main pipe for the 2 upstairs flats with a check valve on each one and some sort of pressure limiter on the bottom and mid flat to create some resistance so water will be available to the upstairs flat even when downstairs is full on? Put a water tank in the loft for top and mid flat? diden't want to do that really as might want to convert the loft later. cheers Chaps... mark

Check your outside stop tap is fully open.

Read the Water Regulations before converting the flats, if the water pressure is low you will need to install a Break tank and a cold Water Booster set to provide adequate pressure & flow,

Back flow of water must be prevented

Hi Buck, yep checked that thanks.
Hi Boilerman2, Cheers for that. I'll have a look at those water regulations. Never heard of the break tank before but looks like it could be a good option with the pump. will check what pressure and volume of water i'm getting there. will read up and see if the loft tank is still a goer as i already have a couple of those hanging around. Thanks very much for the info Chaps.
mark