In Fataawa Mahmoodiya and Fataawa Aalamgiri the following is written;
“When there is no rain, and there are neither wells, rivers, etc., or if there are wells, rivers etc. but they are totally dry, or if they have water but there is insufficient water to satisfy the basic needs (of the people, animals and crops); that is, there is insufficient water to drink, give animals or for the crops, only then is Salaatul Istisqaa prescribed by the Shariah. If there is sufficient water (to satisfy the basic needs) then Salaatul Istisqaa is not prescribed.
‘And according to the Shariah, seeking rain (Salaatul Istisqaa) is only (performed) under special circumstances, when there is severe need (shortage/non-existence of water), and the rain has been withheld; such that they do not have rivers, wells, reservoirs, etc. wherefrom they may drink, give their animals or water their crops. Or if there are these (sources of water) but they are insufficient to fulfil their basic needs.
If there is sufficient (water, albeit no rain), they should not make (Salaatul Istisqaa). As mentioned in Muheet.’ [Raddul Muhtaar, vol.1, page 883]
When the situation is so dire, then Salaatul Istisqaa will be valid and permissible, because when there is no vegetation, then the animals will have no fodder and they will perish.”
[Fataawa Mahmoodiya, vol. 7, page 141]
“And Istisqaa is only performed in such places where there are no water reservoirs, rivers or wells, wherefrom people may drink, give their animals to drink or water their crops. Or if these (water sources) are available; but the water is insufficient. If there are water reservoirs, rivers and wells, then they should not go out for Salaatul Istisqaa, because this is only performed at times of severe shortage and desperate need. This is recorded in Muheet.”
[Fataawa Aalamgiri, vol. 1, page 394]
Source - Al Islam