New Property with Existing Tenants

[Daniel Leathers]

Hello, 

My wife and I just purchased a duplex in the very tenant-friendly City of Los Angeles. One of the units has existing tenants who indicate they want to remain in their unit for the long haul. We have the signed estoppel stating that 1) they did not put down a security deposit and 2) the water & sewage is paid by the landlord. 

When we signed the new lease agreement can we legally stipulate that:

 1) the tenants need to pay and extra $200 per month for 7 months so that we have a deposit?

2) can we charge an amount separate from the rent to offset the cost of the water & sewage?

Thank you for your time and consideration.