Como dizer "Beber água no almoço" em inglês

That sounds much wiser to me, Donay! Thank u!

Anita,

Eu sugiro "while having"

Drink water while having lunch, dinner.
Drink water while having meals.

Do not drink water while having meals.(waystoloseweightfast.co.uk)

Boa sorte!

We normally say any of the following:

She drinks (has) only water AT dinner.(or)
She drinks (has) only water WITH dinner / breakfast / supper / lunch.
She drinks (has) only water WITH her meals.
She has only water at mealtime.

Regards

How about "She often/always washes down her dinner"?

The washing down implies following up one's dinner/lunch with water or another liquid. Some individuals may prefer not to drink water at all. Or prefer to drink it an hour later after dinner/lunch.

Quite frankly, a quick net search did not unearth any of the sentence examples I gave, not one using any of the modifiers "always" or "often."

She drinks water for dinner está correto.

Não entendi o q está estranho ou errado pra vc.
A expressão é "for" e o nome da refeição, não importa se é algo de comer ou de beber.

O uso do "AT" antes das refeições se dá na seguinte hipótese: para falar de alguém q está fazendo aquela refeição.
Ex.: I’m sorry, the person you want to talk is at lunch.

Exemplo do uso do "for":

I eat meat and rice and I drink Coke for lunch.

Espero ter ajudado.

Anita, I agree. If "you drink water for lunch", I am hearing that your entire lunch consists of water, no solids.

If "you have water and a hamburger for lunch", then I am hearing that for lunch you eat a hamburger and drink water.