Weak water pump or small water output

It often occurs in the water pump impeller made ​​using brass. Hand side of the impeller is easily eroded sand which resulted in a wide cavity between closed impeller, impeller, and pump blog. And the effect of the pump suction becomes weak ..
With the replacement of the impeller cap and Impellernya problem can be resolved while his blog is not severe. Another way to do the patching, but sometimes not preserved, only a few months back already weak.
Another way to flatten the back cover with the manner in Lathe impellernya, but the cost is too expensive. Not according to the price of the water pump.