database for water metering

[iznubadd]

hi
i have an apartment and we have main water metering facilities, from that main we distribute it individually with their respective water metering. I want to have an individual records to monitor each occupant's water usage. I have this trouble building table with running balance. How can i implement that?

sample....
Rental Room #5 usage:

Month Reading Usage
Oct       125     0
Nov       236   111
Dec       298    62
Jan        345   47

Pls help or suggest table structure design.