It was the Finn's 10th appearance for Williams in Friday practice and he ended the session eighth fastest overall.
His Spa performance continued an impressive run, during which he has often outpaced team-mate Pastor Maldonado, suggesting that he is potentially the fastest of Williams's three drivers in terms of pure pace.
"Every kilometre with these cars, even in wet conditions, is always about learning at the moment," said Bottas when asked by AUTOSPORT how useful the session was.
"It was nice to experience Spa, even though it was wet. Still, it was really challenging.
"We are always trying to get some running in no matter what the weather is. I just need to take care that I bring the car back in one piece. We were trying to get some laps in."
Bottas added that he was frustrated that rain has hit so many of his outings so far this season.
But despite that, he believes that the experience he is building will help him next year.
With the remaining nine races of the season taking place over 13 weekends, he is hoping that being in the car so regularly will also help him to build momentum.
"I think it has been a little bit unlucky," he said. "Most of the weekends, there has been a bit of rain on the Fridays.
"But we have still got some laps in every session. If you look at today, second practice was even worse than the first so maybe I was a bit lucky.
"[The regularity of races] helps me in my situation because I'm not getting so many laps. The closer the races are together the better it is for me to keep the feeling of driving.
"I'm looking forward to it, also to see what it's like with the travelling and the jetlag."