Baby 10 months old

My Health Visitor told me to lessen the formula now my baby will be 10 months tomorrow. They suggested dropping the milk feed after lunch and just giving him a lot more water. I’m a bit concerned. I said he consumes about 500ml formula and still eating 3 meals a day but she said if he carries on with 500ml he could become malnourished as it’s filling him up too much. He eats a very varied diet now with plenty of fresh fruit, meat, fish and vegetables. I’m from the U.K. so I looked on the NHS website and it states he should be having about 400ml a day at least. What is your advice? Thanks