This was the second time Mr Trump has taken the stage at the WEF meeting.
The summit in the Swiss Alpine town runs through January 24.
In his 30-minute opening remarks, Trump spent most of the time listing his achievements, including tax reform, regulatory rollback, trade deals, and record unemployment rate.
Swedish climate activist Greta Thunberg inveighed against the sowers of "climate chaos" at the World Economic Forum in Davos, Switzerland, on Tuesday, offering a view of the world that stood in stark contrast to President Trump's.
Trump told the World Economic Forum at Davos this week that the U.S. has "among the cleanest air and drinking water on Earth", despite widespread contamination with chemicals such as PFAS and neurotoxins such as lead in Americans' water.
Trump was also asked why he has claimed that no Americans were affected by Iran's retaliatory missile strikes following the US operation that killed former Gen. Qassem Soleimani, given that 11 USA servicemen were airlifted with injuries.
A draft version of the rule released earlier would end federal oversight for up to half of the nation's wetlands, which provide buffers against flooding and climate change, and one-fifth of the country's streams, the upstream sources of drinking water, environmental groups warned.
President Trump has touted that farmers are set to benefit the most from the overhaul, according to AP, which notes farmers are "a highly valued constituency of the Republican Party and one popular with the public".
The hall was packed, the overflow rooms were packed, but Trump told them what he came to tell - not the message of global togetherness and environmental healing that many of them wanted to hear.
"Our water numbers, our numbers on air, are tremendous", he said.
Iraq's parliament passed a resolution urging the government to expel USA troops from the country, prompting Trump to respond with a threat not to leave unless Iraq reimburses the United States for a US airbase there.
Nobel Prize-winning economist Joseph Stiglitz criticised the President's swipe at climate "pessimists". "Meanwhile we're going to roast".
The White House says the change will be a victory for American farmers.
Trump did not rule out imposing tariffs on European cars if both sides failed to reach a trade agreement.
Trump has repeatedly directed administration officials to defy subpoenas for documents and testimony, but he said Wednesday that he would "love to have" them appear before Congress.
The US president arrived in Davos with the fixings on his brogues.
For 25 years he had the ear of world leaders, CEOs and even rock stars at Davos, but the Swiss ski resort's most-listened to man has moved on.
Maintaining that balance became trickier for Baghdad after an escalation that began last month with rockets fired at a US base in Iraq, killing an American contractor, and reached its peak with the drone strike that killed Soleimani.