How to model underground water tanks in water system instead of junctions

Hello ever one ;

I have a water network that have 15000 houses ,

Each customer has underground water tanks which they are connected directly to the water network ,

Those water tanks have different storage capacity (varying from 10m3 to 200 m3) based on the usage type (small housing unit , hotels .... etc),

The reason for connecting those tanks directly to the network is the shortage between the demanded and daily supplied amount of water ,

So based on daily supplied water the city was divided into separated sections and then the water is discharged to each section based on weekly schedule

for example area#1 will get its demand on Saturday for 7 hours and then will be supplied with water again on Tuesday for 7 hours and so on for other districts

My question is how to model those tanks on watercad to match real situation  .

Thanks