Splitting Utility Bills between two tenants

[Prabhu Babu]

Hello fellow tenants & landlords,

I hope everyone is sound and safe. I recently moved into a Single Family Home in Mountain View, CA. My landlord has sublet a portion (upstairs) for another person. The other tenant is staying in that sublet portion for many years. Before signing the lease agreement, when my landlord told me that utilities are the tenant's responsibility, I thought he was referring to only my portion of the home, it was common sense, I accepted and signed the lease agreement. I received my utility bills a week ago. It was so high. I was concerned and so I checked if there are separate meters for Electricity/Gas and Water. But to my surprise, there was only one meter. Then I called my landlord to understand the details. He is initially claimed that I agreed to pay for utilities for another person too. I disagreed, why would I agree and pay for another person's utilities. Then he came down a bit, saying that other tenant's usage is very less, it is negligible, etc. He also apologized for the miscommunication towards the end of the call. 

Relationship between my landlord and me: This landlord was my real estate agent when I bought my first home (rented recently) 5 years ago. I never thought he would do this to us. I expected him to be very open and declare the details in the lease agreement.

My portion was vacant between Dec 16th, 2019 and Jan 31st, 2020. My lease started on Feb 1, 2020. I requested him to share the utility bills for the months before I moved in. So that we can understand the usage of the other tenant for all the utilities. He promised to send those bills in the next two days.

After reviewing the previous months' usage, for the next steps, I'm considering the following:

1. For every month, divide the total utility bills amount by total headcount (including the other tenant). Deduct the other tenant's share of the bill amount from my subsequent monthly rent.

2. Ask my landlord to create an addendum with the above details and attach it to our existing lease agreement.

I learned my lesson from this bitter experience.  I decided to be more alert, so please share any other suggestions, things to be careful, better ways, to handle this situation. 

Thank you in advance for sharing your thoughts.