First, the waterchestnut flour must be genuine, there are some fake ones,
Second, cook the batter until it is thickened before steaming it, this step would stablize it and prevent breaking down and watery.
Or you can add a little wheat starch (Tang flour)
That would be the batter alone, you would need to add a lot of diced water chestnuts into the batter.
Superstore have 1 Kg pack fresh water chestnuts for $1.99 .
Labour cost, that is why some bakeries put frozen corns into water chestnut cake to save labour.
The water chestnut have to be fresh, The canned one taste terrible