Liam Walter, 5, of Figtree, has a disorder known as nephrogenic diabetes insipidus, which interferes with his kidney's ability to conserve water.

Sufferers urinate on average every half an hour and need to constantly replenish their fluids.

Liam, who was diagnosed at 12 weeks, must have easy access to water day and night as his thirst is unrelenting and intensifies if he eats foods containing salt.

"He has just started school and has to carry a large water bottle around his neck that he fills constantly during the day," his mother Sherin said.

Apart from a low-salt diet and 12 lots of daily medication, there is not much Liam or his parents can do to relieve the symptoms.

However, Mrs Walter said his plight could be vastly improved if there were more low-salt products on supermarket shelves.

"Liam's condition is rare, but there are tens of thousands of people who would benefit from low-salt diets and there is so little for them in terms of food products," she said.

Mrs Walter said Australia was lagging behind countries such as the United States, which - according to her research - has supermarkets dedicated to low-salt food products.

"We have plenty of gluten-free products available, but for kids like Liam it's either deprivation or suffer the consequences of eating salty foods," she said.

"Something as simple as a low-salt snack or kiddies' cereal would be appreciated by families like ours."

Mrs Walter said it was getting harder for Liam, who is now out mixing with other kids and wants to fit in.

"A small sausage roll will send him running to the tap until he's so bloated he vomits," she said.

"But we have to step back and let him discover what he can and can't eat - it's too distressing to ban everything and it wouldn't work."

Mrs Walter tries to cook low-salt alternatives to everyday food products but even bicarb soda in cakes has enough sodium to intensify Liam's thirst.