If they aren't drinking, your heifers aren't eating. And if they aren't eating, they aren't growing. Clean drinking water is key for all pastured cattle. For, heifers, it's a vital link in the chain of successful growth.
Water quality affects consumption.
If your heifers' water intake is low, they'll eat less dry matter. Low consumption reduces growth. To maximize their water and feed intake, you need to provide them with clean, palatable water. Pastured livestock are often watered from surface sources. Water quality deteriorates if you let cattle walk into the water or let surface runoff containing fecal material contaminate it.