After a sparkling end to the last campaign, the Finn admits both he and the team had hoped for more in 2015, but insists the team can still find improvements and move back toward the front of the field. He and team mate Felipe Massa have been restricted to just two collective podiums so far, compared with five at the same stage last year.
"I do admit we expected more from this year's car, particularly in the first part of the season and if you compare it with 2014, then we had a few more podiums at this time of the year than we have now," Bottas said in a blog on Williams' official website.
"Having said that we are still capable of improving and getting closer to Ferrari - so I will be looking to secure more podiums in the second half of the season.
"I think Williams is a great team to be with, and I'm confident they can be up there again in 2016. There's no reason why Williams shouldn't be able to be fight with Ferrari and Red Bull."
Bottas also reiterated that much of the media speculation linking him with a 2016 switch to Ferrari had been incorrect, and that he had largely ignored the rumours over the summer break.
"Until the week before Spa there was a lot of speculation about my future, a good part of which was not true," he added. "It's not fair to put those kind of rumours out there, for either Williams and myself or Kimi and Ferrari, so life became easier once we knew the speculation was over with Kimi staying where he is.
"I have to say the speculation didn't affect me at all during the break because I wasn't reading or listening to anything vaguely connected to Formula One, which was really good. Then I saw the news on Wednesday and that was that - end of story. In Belgium… we got down to the business I'm here for - racing."