No result means the three-match series was tied at 1-1 after South Africa won the first ODI by 62 runs with England rebounding to win the second by 118 runs.
South Africa won the toss on Sunday and elected to bat with De Kock 69 not out before the first break for rain. When the teams returned for another seven overs, he moved onto 92 not out before rain fell again, leading to a decision to abandon the contest.
South Africa were 159-2 from 27.4 overs.
The two countries now meet in three Twenty20 internationals, starting in Bristol on Wednesday.
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