12 volt DC to 12 volt AC sine wave inverters for 10 watt and 22 watt pumps
The simplest and probably the cheapest way to go is to purchase an automotive 12 volt inverter to convert the 12 VDC to 120 VAC.  Then use a 120 VAC to 12 VAC power transformer to convert the inverter output to 12 VAC. The waveform out of most inverters is not sinusoidal although after going through the transformer its waveshape will probably improve since the transformer has limited bandwidth.  If you need a sine wave, you can purchase a higher quality inverter.