Diluting paint with water can improve paint flow but it should be done sparingly. Over-diluting water-based paint reduces its ability to cover flaws and stick to a surface. Water dries at a slower rate than paint and can alter the drying time specified on the product label. The water-to-paint ratio can vary from one product to the next, so finding the dilution or thinning recommendations on the product label is recommended. Around 50 ml (1/4 cup) of water per 4.5 litres (1 gallon) of water-based paint is a viable ratio because it is minimal. Adding more water than this might mean you need to use several coats of paint.
Spread newspapers or a plastic sheet over your work area to protect it from paint spills and splatter.
Consult the label on the paint tin for the manufacturer's recommended dilution ratio. Pour the correct quantity of water into the bucket, and then add the water-based paint to the same bucket.
Mix the paint with the water for several minutes until they are thoroughly mixed, using a stir stick. When you've got the right consistency, apply the water-based paint.
Follow the diluting or thinning directions on the label of the paint product for appropriate water-to-paint ratios.