In atrocious conditions of driving rain and a strong wind, both teams came close to breaking the deadlock.
O's keeper Jamie Jones fully extended to deny Alan McCormack's long-range effort and Andy Williams hit the crossbar, while Swindon's Wes Foderingham produced a splendid save to deny substitute Jimmy Smith's full-blooded drive from 10 yards.
"Nobody played for a draw and I thought that conditions were probably the winner in the end to be honest," Slade stated. "I thought that their keeper pulled off a really, really good save from our substitute Jimmy Smith right at the end to keep it at 0-0 because it was a really good opportunity.
"I thought they had the better of the first half and I thought we came more into it in the second period and looked a lot more of a threat. We played the conditions a lot better in the second half."
Swindon manager Paolo Di Canio was less than pleased with the draw, saying: "I'm very disappointed. We have to step back and look at ourselves in terms of desire even if we did look like the better team in the first half. I am talking in terms of individuals, not the whole team.
"The pitch was not good but we played some good football and we should have scored a goal. We created a few chances but when you don't score, you have the risk of losing.
"From the fans point of view, they probably think there is nothing wrong because we are making chances but I'm very disappointed with some of the players and I will tell them who and why and obviously we will have a look at the situation."
Di Canio also admitted he needs to dip into the transfer market before Thursday's deadline to boost his attacking options.
He said: "We need to go into the transfer market. I need to play players with genuine attitude. We look like a team that will score"