Havoc, there is no law about how much your residential rent can be increased each year.
There used to be a law, but the government cancelled it, so your landlord is free to double your rent for your apartment or villa if he wishes.
Theoretically non-residential leases are supposed to be limited to the following increases:

20% per year if the rent value is less than QAR 3,000;
15% per year if the rent value is between QAR 3,000 and 6,000;
10% per year if the rent value is between QAR 6,000 and QAR 10,000;
5% per year if the rent value is more than QAR 10,000.