It comes as the TGA's Brown Lawns are Cool campaign hit headlines, reinforcing the message that established lawns do not need to be watered.
TGA chief executive Tim Mudge said: "We are pleased that water companies have acted so swiftly and delighted that they have taken on board what we have said in the code of practice."
A United Utilities representative said the company was committed to the measure. "Anyone who has newly-laid turf and plants put in by a contracted gardener is exempt for 28 days," he said. "We have been advised that this gives enough time for plants to take root."
Mudge said the TGA had contributed to the discussions on water regulation for many years and would continue to seek discussions in a bid to see the new Flood & Water Management Bill come into force as quickly as possible.
He pointed out that the exemption came as a welcome reprieve to turf growers who have been struggling against tough economic conditions for the past two years.
"It's a tough time out there because of the economic situation," he confirmed. "Those that have been heavily reliant on development have had to switch their attention to other forms of landscaping such as more small, private projects."
He added that the ban had come at a crucial time in the turf growers' year and said he hoped that the exemption would help to "limit the drop in demand".
While working with the water companies, the TGA has also been promoting its campaign to raise public awareness that established lawns do not need watering.
Mudge has appeared on BBC and ITV news features to discuss the Brown Lawns are Cool campaign. He said public awareness was growing but there was still work to be done because turf sales continue to suffer in periods of prolonged heat.
"Our message to homeowners is not to worry if your lawn goes brown during the summer. Going brown is the natural survival mechanism of grass," he explained.
"When water is in short supply grass responds by shutting down. The brown colour shows that it has stopped growing until more favourable conditions return. Grass is remarkably resilient and as long as you follow a few basic rules, most lawns will recover completely when the rain finally arrives."
TGA DROUGHT TIPS
- Increase your mowing height to 35-40mm to create deeper roots and more shade and shelter from higher temperatures.
- Try not to concentrate wear in one place - move barbeques and toys such as slides around.
- No need to feed because grass will not be growing during hot, dry weather.
- Avoid blanket weedkillers because these may damage the grass - use a spot weedkiller if necessary.
- Keep mower blades sharp - blunt blades bruise the grass leaf and it loses more water.
- Apply a light dressing of compost to help keep moisture in the soil and protect grass from higher temperatures.
- Scarify your lawn once a year to remove matted and dead growth - if allowed to build up, this acts as a barrier to rainfall.