"You had a lot of rain at that particular time, that may have been a factor and it may not, I just simply don't know.
"If the contamination of the water came because there was heavy rainfall then we need to do something to ensure that it can withstand heavy rainfall, not spend our life worrying about climate change."
In response, Mr Shaw said what was dangerous was not considering the possible connection between climate change and the outbreak, "because you specifically exclude whole areas of investigation".
"Then you are actually deliberately missing out on information that may be important in terms of avoiding these kinds of outbreaks in the future, not just in Hawke's Bay but around the rest of the country," he said.
If climate change was connected with the outbreak, the possibility needed to be taken into account that similar incidents would happen on an increasing frequency in future.
Water supplies in Hawke's Bay would need to be future-proofed, he said, which could only happen if the future risks to water quality, which stemmed from a variety of causes including climate change, were addressed.
"If you deliberately set the terms of inquiry so narrow that you only find the solution that you want to find, that actually ... devalues the whole inquiry," he said.
He said, "not only is [Mr Key] not taking a wide enough approach to the inquiry, he's actually deliberately staying away from things that may be directly relevant, thus placing other communities at risk."
When asked why he thought this might be, Mr Shaw said he thought the Prime Minister was worried looking at this connection could implicate the agricultural sector.
"He doesn't want anything to undermine the reputation of that sector, even though scientifically that is the causal relationship," he said.
In response to Mr Shaw's comments, a spokeswoman from the Prime Minister's office said: "we don't know how the water supply became contaminated and we don't want to speculate, that's why we have launched an inquiry to find out".
She said the inquiry, headed by the Honourable Lyn Stevens QC, would focus on how the water supply became contaminated, how this was addressed, and how local and central government agencies responded to the public health outbreak that occurred as a result of the contamination.
It would also focus on how to reduce the risk of outbreaks of this nature recurring, and consider any necessary changes to prevent or minimise similar incidents in the future.
"I think the key point here is we don't want to jump to conclusions. We want to wait and see what comes out of the inquiry," she said.
Tukituki MP Craig Foss said the Hawke's Bay Regional Council and government needed time to investigate in their respective inquiries.
He agreed with Mr Shaw's statement that the recommendations and outcomes of the inquiry needed to be considered and implemented at a nationwide level.
Mr Foss said, "we must find out why this happened and stop it from ever becoming an issue again, for the health and well-being of our families and community, as well as our businesses."